From BiblePortal Wikipedia

Hastings' Dictionary of the New Testament [1]

(Δημᾶς, perhaps a short form of Demetrius, as Silas was of Silvanus)

Demas was a Christian believer who was with St. Paul during his imprisonment in Rome, and sends greetings to the Colossians ( Colossians 4:14) and to Philemon ( Philemon 1:24). Probably he was a Thessalonian, and in both the references he is mentioned in connexion with St. Luke, while in  2 Timothy 4:10 his conduct is contrasted with that of the beloved physician, In the last-named passage we are informed that Demas left the Apostle when he was awaiting his trial before Nero. The desertion seems to have been deeply resented by St. Paul, who describes his action as due to his ‘having loved this present world.’ Probably Demas realized that it was dangerous to be connected with one who was certain to be condemned by Nero, and he saved his life by returning to his home in Thessalonica. The phrase used, however, suggests that the prospect of worldly advantage was the motive which determined Demas. No doubt the busy commercial centre of Thessalonica offered many opportunities for success in business, and love of money may have been the besetting sin of this professing Christian. The name ‘Demetrius’ occurs twice in the list of politarchs of Thessalonica; and, while we cannot say with certainty that the Demas of  2 Timothy 4:10 is identical with either of these, the possibility is not excluded. In this case the prospect of civic honours may have been the reason which led him to abandon the hardships and dangers of the Apostle’s life and return to Thessalonica, where his family may have held positions of influence. Perhaps the bare mention of his name in  Colossians 4:14 and the reference in  Philippians 2:20-21 may indicate that the Apostle even at this early date suspected the genuineness of Demas, who was with him at the time of his writing to Philippi (cf. Ramsay, St. Paul , p. 358). We have no certain assurance that the apostasy of Demas was final, but the darker view of his character has usually been taken, as e.g. by Bunyan in The Pilgrim’s Progress . Epiphanius ( Haer . li. 6) classes him among the apostates from the faith. It is impossible to identify Demas with any Demetrius mentioned in the NT.

Literature.-W. M. Ramsay, St. Paul the Traveller and the Roman Citizen 3, 1897. p. 358; J. B. Lightfoot, Colossians and Philemon 2, 1876, pp. 36, 242; articles in Hasting's Dictionary of the Bible (5 vols) , Encyclopaedia Biblica , and Hastings’ Single-vol. Dictionary of the Bible .

W. F. Boyd.

Fausset's Bible Dictionary [2]

Contracted from DEMETRIUS, or Demarchus. Paul's "fellow laborer," along with Mark and Luke ( Philemon 1:24), and companion ( Colossians 4:14) during his first Roman imprisonment. But he declined; for in  2 Timothy 4:10 Paul writes, "Demas hath forsaken (Greek text: "left behind") me, having loved this present world (world course), and is departed unto Thessalonica," probably his home (Chrysostom). Love of worldly ease and home comforts was his snare, a sad contrast to "all them that love Christ's appearing" ( 2 Timothy 4:8).

Smith's Bible Dictionary [3]

De'mas. (Governor Of The People). Most probably, a contraction from Demetrius , or perhaps from Demarchus, a companion of St. Paul,  Philemon 1:24;  Colossians 4:14, during his first imprisonment at Rome. (A.D. 57). At a later period,  2 Timothy 4:10, we find him mentioned as having deserted the apostle through love of this present world, and having gone to Thessalonica.

Hastings' Dictionary of the Bible [4]

DEMAS (= Demetrius?). A companion of St. Paul in his first Roman imprisonment (  Colossians 4:14 ,   Philippians 1:24 ). There is some indication (cf.   Philippians 2:20 f.) that even then Demas was not altogether trusted; and later he forsook the Apostle, ‘having loved this present world’ (  2 Timothy 4:10 ). He was apparently a native of Thessalonica.

A. J. Maclean.

Morrish Bible Dictionary [5]

Fellow-labourer with Paul at Rome,  Colossians 4:14;  Philippians 24; of whom Paul had to write some five years later, "Demas hath forsaken me, having loved this present world, and is departed to Thessalonica."  2 Timothy 4:10 . This may signify, not that he had apostatised, but that he had fallen from Paul's line of things through love of this present age.

People's Dictionary of the Bible [6]

Demas ( Dç'Mas ). Probably contracted from Demetrius. A companion of Paul during his first imprisonment at Rome.  Colossians 4:14; Philem. 24. The mournful note is subsequently made that he had forsaken the apostle, "having loved this present world."  2 Timothy 4:10. Whether this meant actual apostasy we know not.

American Tract Society Bible Dictionary [7]

A fellow-laborer with Paul at Thessalonica, who afterwards deserted him, either discouraged by the hardships of the work, or allured by the love of the world,  Colossians 4:14   2 Timothy 4:10   Philippians 1:24 .

Holman Bible Dictionary [8]

 Colossians 4:14 Philippians 1:24  2 Timothy 4:10

Easton's Bible Dictionary [9]

 Philippians 1:24 Colossians 4:14 2 Timothy 4:10

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [10]

( Δημᾶς , probably a contraction from Δημήτριος , or perhaps from Δήμαρχος ), a companion of the apostle Paul (called by him his fellow- laborer, Σύνεργος , in  Philemon 1:24; see also  Colossians 4:14) during his first imprisonment at Rome. B.C. 57. At a later period ( 2 Timothy 4:10), we find him mentioned as having deserted the apostle through love of this present world, and gone to Thessalonica. B.C. 64. This departure has been magnified by tradition into an apostasy from Christianity (so Epiphanius, Haeres. 51:6), which is by no means implied in the passage (Buddei Eccl. Apost. p. 311 sq.).

International Standard Bible Encyclopedia [11]

dē´mas ( Δημᾶς , Dēmás , "popular"): According to  Colossians 4:14;  2 Timothy 4:10;  Philippians 1:24 , one who was for a time a "fellow-worker" with Paul at Rome (Col, Philem), but at last, "having loved this present world," forsook the apostle and betook himself to Thessalonica (2 Tim). No other particulars are given concerning him. See Apostasy; Demetrius .

Kitto's Popular Cyclopedia of Biblial Literature [12]

De´mas, a Thessalonian Christian who was for a time associated with St. Paul, but who afterwards abandoned him at Rome, either from being discouraged by the hardships and perils of the service, or in pursuit of temporal advantages (;; ).