From BiblePortal Wikipedia

Hastings' Dictionary of the New Testament [1]

(Ἰουλία,  Romans 16:15, a Latin name, the feminine form of Julius [the name of a famous Roman gens]. Both of these were extremely common names. The name Julia is very frequently found as a name of female slaves belonging to the Imperial household)

A woman saluted by St. Paul and coupled with Philologus. They may have been brother and sister, or more probably husband and wife. Other couples saluted in Romans 16 are Aquila and Prisca ( Romans 16:3, the order being, however, ‘Prisca and Aquila’), perhaps Andronicus and Junia ( Romans 16:7; see Junias), and Nereus and his sister ( Romans 16:15). It has been conjectured that the names in this verse are those of persons forming a Christian family with a household church (καὶ τοὺς σὺν αὐτοῖς πάντας ἁγίους). If this be so, Philologus and Julia were perhaps the parents of Nereus and his sister (Nerias) and Olympas, and the leaders of the little community which gathered for worship at their home (cf.  Romans 16:3, where a married couple are saluted as ‘fellow-labourers’ with the Apostle, and the salutation includes ‘the church which assembles at their house’). The locality to which we assign this circle of Christians will depend upon our view of the destination of  Romans 16:3-20. Nothing further is known of any of these persons.

T. B. Allworthy.

Fausset's Bible Dictionary [2]

A Christian woman at Rome, whom Paul salutes ( Romans 16:15), wife or sister of Philologus. Julius. Centurion of "Augustus' band" (a detachment probably of the emperor's praetorian body guards, attached to the Roman governor at Caesarea); had charge of Paul from Caesarea to Rome ( Acts 27:1;  Acts 27:3). As all the centurions in New Testament, so Julia was an estimable character. He "courteously gave Paul liberty to go unto his friends to refresh himself." God raises friends to His people even among enemies.

Smith's Bible Dictionary [3]

Ju'lia. (feminine of Julius ). A Christian woman at Rome, probably the wife of Philologus, in connection with whom she is saluted by St. Paul.  Romans 16:15. (A.D. 55).

Hastings' Dictionary of the Bible [4]

JULIA. A Christian greeted by St. Paul in   Romans 16:15 , perhaps a ‘dependent of the Court,’ and wife or sister of Philologus (Lightfoot, Phitipp . p. 177).

A. J. Maclean.

Morrish Bible Dictionary [5]

Christian woman at Rome to whom Paul sent salutations.  Romans 16:15 .

Holman Bible Dictionary [6]

 Romans 16:15

Easton's Bible Dictionary [7]

 Romans 16:15

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [8]

( Ι᾿Ουλία , fem. of Julius ) , a Christian woman of Rome, to whom Paul sent his salutations ( Romans 16:15); she is named with Philologus, and is supposed to have been his wife or sister. A.D. 55. Kitto. "Origen supposes that they were master and mistress of a Christian household which included, the other persons mentioned in the same verse. Some modern critics have conjectured that the name may be that of a man, Julias"

International Standard Bible Encyclopedia [9]

jōō´li - a ( Ἰουλια , Ioulı́a ): The name of a Roman Christian to whom Paul sent greetings, the wife or sister of Philologus with whose name hers is coupled (  Romans 16:15 ). The name points to member of the imperial household.

Kitto's Popular Cyclopedia of Biblial Literature [10]

Ju´lia (a name common among the Romans), a Christian woman of Rome, to whom St. Paul sent his salutations she is named with Philologus, and is supposed to have been his wife or sister.

The Nuttall Encyclopedia [11]

Daughter and only child of Augustus Cæsar; celebrated for her beauty and the dissoluteness of her morals, and became the wife in succession of Marcellus, Agrippa, and Tiberius.