Hastings' Dictionary of the New Testament 
This is the name of a Christian convert belonging to Ephesus who had visited Rome during the apostle Paul’s imprisonment and had sought out the prisoner and ministered to his wants: ‘He off refreshed me, and was not ashamed of my chain’ ( 2 Timothy 1:16). He had also performed outstanding services for the Church at Ephesus, to which the Apostle refers, mentioning that Timothy, to whom he writes, knew better (βέλτιον) about them than he did himself ( 2 Timothy 1:18). The word used here and translated ‘ministered’ (Gr. διακονέω) has been supposed to indicate that Onesiphorus acted as a deacon of the Church in Ephesus, but this is by no means certain. When in Rome during his second imprisonment the Apostle sends greetings to the household of Onesiphorus ( 2 Timothy 4:19); and in 2 Timothy 1:16 he expresses the desire that the Lord may give mercy to the ‘house of Onesiphorus.’ St. Paul mentions that Onesiphorus had treated him very kindly when in Rome, and contrasts his action with that of other members of the Church of Asia, who had turned away from him and refused to help him in his need, particularly referring to Phygellus and Hermogenes.
Several questions arise here. Why does St. Paul speak of the household of Onesiphorus? Why does he not send greetings to Onesiphorus himself, as he does, e.g., in 2 Timothy 4:19 to Prisca and Aquila? Was Onesiphorus dead when the Epistle was written? Most students conclude that Onesiphorus had already died. If this view be correct, an interesting point arises with regard to the prayer in 2 Timothy 1:18 -‘the Lord grant unto him that he may find mercy of the Lord in that day.’ Is this a prayer for one who was already dead? Several who advocate the practice of prayer for the departed have quoted this passage in support of their position (e.g., Archibald Campbell, The Intermediate or Middle State of Departed Souls, London, 1713, p. 72; E. H. Plumptre, The Spirits in Prison, do., 1884, pp. 128, 266; H. M. Luckock, After Death3, do., 1881, p. 77, The Intermediate State2, do., 1896, p. 211). N. J. D. White, in Expositor’s Greek Testament, ‘1 and 2 Timothy and Titus,’ London, 1910, p. 159, refers to 2 Maccabees 12:44 in support of the contention that an orthodox Jew of the time of Christ could have prayed for the dead. It seems, however, to be an undue pressing of the text to regard the sentence in 1:18 as more than a pious wish on the part of the Apostle for. one of whom he had very kindly memories (cf. G. S. Barrett, The Intermediate State, London, 1896, p. 113). In any case, we have no foundation whatever for the Roman Catholic system of prayers for the deliverance of souls from the pains of purgatory.
See, further, articles in Hasting's Dictionary of the Bible (5 vols)and Encyclopaedia Biblica.
W. F. Boyd.
Fausset's Bible Dictionary 
2 Timothy 1:16-18; 2 Timothy 4:19; "the Lord give mercy unto the house of Onesiphorus (As Onesiphorus Showed Mercy) , for he oft refreshed me and was not ashamed of my chain (compare Matthew 25:36; Matthew 25:45), but when he was in Rome he sought me out very diligently and found me. The Lord grant unto him that he may find mercy (as he found me) of the Lord in that day; and in how many things he ministered unto me at Ephesus thou knowest very well." "Salute the household of Onesiphorus" ( 2 Timothy 4:19).
Absence from Ephesus probably is the cause of the expression; he had not yet returned from his visit to Rome. If the master were dead the household would not be called after his name. A good man's household shares in his blessing from God as in his deeds for God. Nowhere does Paul use prayers for the dead; Onesiphorus therefore was not dead. "The household of Stephanas" does not exclude "Stephanas" ( 1 Corinthians 1:16; 1 Corinthians 16:17) so "the household of Onesiphorus" does not necessarily exclude Onesiphorus.
Hastings' Dictionary of the Bible 
ONESIPHORUS . The name of a Christian mentioned twice in St. Paul’s Second Epistle to Timothy ( 2 Timothy 1:15-18; 2 Timothy 4:19 ). From the first reference we learn that he showed special kindness to the Apostle during his imprisonment at Rome, when others, from whom he might have expected sympathy and help, held aloof from him; from the second we infer that he and his family lived at Ephesus. From St. Paul’s expression ‘the household of Onesiphorus,’ it has been inferred that Onesiphorus himself was dead, and this text has been urged in proof of the lawfulness of prayers for the dead. There is much probability in this view, but the breathing of such a pious wish has nothing in common with the later abuses which gathered round this practice.
Smith's Bible Dictionary 
Onesiph'orus. (Bringing Profit). Onesiphorus is named twice only in the New Testament, namely, 2 Timothy 1:16-18 and 2 Timothy 4:19. Paul mentions him in terms of grateful love, as having a noble courage, and generosity in his behalf, amid his trials as a prisoner at Rome, when others from whom he expected better things had deserted him. 2 Timothy 4:16. Probably, other members of the family were also active Christians. 2 Timothy 4:19. It is evident from 2 Timothy 1:18, that Onesiphorus had his home at Ephesus. (A.D. 64).
American Tract Society Bible Dictionary 
A Christian friend of Paul at Ephesus, who came to Rome while the apostle was imprisoned there for the faith, and at a time when almost every one had forsaken him. This is supposed to have occurred during Paul's last imprisonment, not long before his death. Having found Paul in bonds, after long seeking him, he assisted him to the utmost of his power, and without regard to danger; for which the apostle implored the highest benedictions on him and his family, 2 Timothy 1:16-18 4:19 .
People's Dictionary of the Bible 
Onesiphorus ( Ŏn'E-Sĭ'Fo-Rŭs ), Profit-Bringing. A primitive Christian who ministered to the wants of Paul at Ephesus, and afterward sought him out at Rome and openly sympathized with him. 2 Timothy 1:16-18; 2 Timothy 4:19.
Hawker's Poor Man's Concordance And Dictionary 
This person is spoken of by the apostle Paul with honorable testimony, 2 Timothy 1:16. His name is a compound from the Greek, and means to bring usefulness.
Morrish Bible Dictionary 
One who sought out Paul at Rome and ministered to him: Paul commended his household to God. 2 Timothy 1:16; 2 Timothy 4:19 .
Holman Bible Dictionary 
2 Timothy 1:16-18 2 Timothy 1:16 2 Timothy 4:19
Watson's Biblical & Theological Dictionary 
is mentioned, 2 Timothy 1:16-17 , and highly commended by St. Paul.
Easton's Bible Dictionary 
2 Timothy 1:16-18 4:19
International Standard Bible Encyclopedia 
ō - nḗ - sif´ṓ - rus ( Ὀνησίφορος , Onēsı́phoros , literally, "profit bringer" ( 2 Timothy 1:16; 2 Timothy 4:19 )):
1. The Friend of Paul:
Onesiphorus was a friend of the apostle Paul, who mentions him twice when writing to Timothy. In the former of the two passages where his name occurs, his conduct is contrasted with that of Phygellus and Hermogenes and others - all of whom, like Onesiphorus himself, were of the province of Asia - from whom Paul might well have expected to receive sympathy and help. These persons had "turned away" from him. Onesiphorus acted in a different way, for "he oft refreshed me, and was not ashamed of my chain; but, when he was in Rome, he sought me diligently, and found me."
Onesiphorus was one of the Christians of the church in Ephesus; and the second passage, where his name is found, merely sends a message of greeting from Paul, which Timothy in Ephesus is requested to deliver to "the household of Onesiphorus." (the King James Version).
2. Visits Paul in Rome:
Onesiphorus then had come from Ephesus to Rome. It was to Paul that the church at Ephesus owed its origin, and it was to him therefore that Onesiphorus and the Christians there were indebted for all that they knew of Christ. Onesiphorus gratefully remembered these facts, and having arrived in Rome, and learned that Paul was in prison, he "very diligently" sought for the apostle. But to do this, though it was only his duty, involved much personal danger at that particular time. For the persecution, inaugurated by Nero against the Christians, had raged bitterly; its fury was not yet abated, and this made the profession of the Christian name a matter which involved very great risk of persecution and of death.
Paul was not the man to think lightly of what his Ephesian friend had done. He remembered too, "in how many things he ministered at Ephesus." And, writing to Timothy, he reminded him that Onesiphorus's kindly ministrations at Ephesus were already well known to him, from his residence in Ephesus, and from his position, as minister of the church there.
It should be observed that the ministration of Onesiphorus at Ephesus was not, as the King James Version gives it, "to me," that is, to Paul himself. "To me" is omitted in the Revised Version (British and American). What Onesiphorus had done there was a wide Christian ministry of kindly action; it embraced "many things," which were too well known - for such is the force of the word - to Timothy to require repetition.
The visits which Onesiphorus paid to Paul in his Roman prison were intensely "refreshing." And it was not once or twice that he thus visited the chained prisoner, but he did so ofttimes.
3. His Household:
Though Onesiphorus had come to Rome, his household had remained in Ephesus; and a last salutation is sent to them by Paul. He could not write again, as he was now ready to be offered, and his execution could not long be delayed. But as he writes, he entertains the kindest feelings toward Onesiphorus and his household, and he prays that the Lord will give mercy to the household of Onesiphorus.
He also uses these words in regard to Onesiphorus himself: "The Lord grant unto him to find mercy of the Lord in that day." It is not clear whether Onesiphorus was living, or whether he had died, before Paul wrote this epistle. Different opinions have been held on the subject.
The way in which Paul refers twice to "the household (the Revised Version (British and American) "house") of Onesiphorus," makes it possible that Onesiphorus himself had died. If this is so - but certainty is impossible - the apostle's words in regard to him would be a pious wish, which has nothing in common with the abuses which have gathered round the subject of prayers for the dead, a practice which has no foundation in Scripture.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
( Ο᾿Νησιφορος , Profit-Bringing ) , a believer of Ephesus, who came to Rome during the second captivity of Paul in that city (A.D. cir. 64), and having found out the apostle, who was in custody of a soldier, to whose arm his own was chained, was "not ashamed of his chain," but attended him frequently, and rendered him all the services in his power. This faithful attachment, at a time of calamity and desertion, was fully appreciated and well remembered by the apostle, who in his Epistle to Timothy carefully records the circumstance; and,. after charging him to salute in his name "the household of Onesiphorus," expresses the most earnest and grateful wishes for his spiritual welfare ( 2 Timothy 1:16-18; comp. 4:19). It would appear from this that Onesiphorus had then quit Rome (Kitto). It has even been made a question whether this friend of the apostle was still living when the letter to Timothy was written, because in both instances Paul speaks of "the household" (in 2 Timothy 1:16, '''''Δ''''' '''''Ó''''' '''''Η''''' Ἔλεος Ὁ Κύριος Τῷ Ο᾿Νησιφόρου Οἴκῳ ) , and not separately of Onesiphorus himself. If we infer that he was not living, then we have in 2 Timothy 1:18 almost an instance of the apostolic sanction of the practice of praying for the dead. But the probability is that other members of the family were also active Christians; and as Paul wished to remember them at the same time, he grouped them together under the comprehensive Τὸν Ο᾿Ν . Οικον ( 2 Timothy 4:19), and thus delicately recognized the common merit, as a sort of family distinction. The mention of Stephanas in 1 Corinthians 16:17 shows that we need not exclude him from the Στεφανᾶ Οικον in 1 Corinthians 1:16. It is evident from 2 Timothy 1:18 ( Ὅσα Ἐν Ε᾿Φέσῳ Διηκόνησε ) that Onesiphorns had his home at Ephesus; though if we restrict the salutation near the close of the epistle (4:19) to his family, he himself may possibly have been with Paul at Rome when the latter wrote to Timothy. Nothing authentic is known of him beyond these notices. According to a tradition in Fabricius (Lux Evang. p. 117), he became bishop of Corone, in Messenia. I
Kitto's Popular Cyclopedia of Biblial Literature 
Onesiph´orus (profit-bringer) a believer of Ephesus, who came to Rome during the second captivity of St. Paul in that city; and having found out the apostle, who was in custody of a soldier, to whose arm his own was chained was 'not ashamed of his chain,' but attended him frequently, and rendered him all the services in his power. This faithful attachment, at a time of calamity and desertion, was fully appreciated and well remembered by the apostle, who, in his Epistle to Timothy, carefully records the circumstance; and, after charging him to salute in his name 'the household of Onesiphorus,' expresses the most earnest and grateful wishes for his spiritual welfare . It would appear from this that Onesiphorus had then departed from Rome.
- Onesiphorus from Hastings' Dictionary of the New Testament
- Onesiphorus from Fausset's Bible Dictionary
- Onesiphorus from Hastings' Dictionary of the Bible
- Onesiphorus from Smith's Bible Dictionary
- Onesiphorus from American Tract Society Bible Dictionary
- Onesiphorus from People's Dictionary of the Bible
- Onesiphorus from Hawker's Poor Man's Concordance And Dictionary
- Onesiphorus from Morrish Bible Dictionary
- Onesiphorus from Holman Bible Dictionary
- Onesiphorus from Watson's Biblical & Theological Dictionary
- Onesiphorus from Easton's Bible Dictionary
- Onesiphorus from International Standard Bible Encyclopedia
- Onesiphorus from Cyclopedia of Biblical, Theological and Ecclesiastical Literature
- Onesiphorus from Kitto's Popular Cyclopedia of Biblial Literature