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.
Kitto, John, ed. Entry for 'Onesiphorus'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/o/onesiphorus.html.