Onesimus (d. 68) means useful. In the New Testament, Onesimus was a slave who, after robbing his master Philemon at Colosse, fled to Rome, where he was converted to following Christ through the witness of the apostle Paul, who sent him back to his master with the epistle which bears his name. In it Paul asks Philemon to receive his slave as a "faithful and beloved brother." Paul offers to pay to Philemon anything his slave had taken, and to bear the wrong he had done him. He was accompanied on his return by Tychicus, the bearer of the Epistle to the Colossians (Philemon 1:16, 18).

Paul makes a pun on "useful".

According to Easton's Bible Dictionary, "The story of this fugitive Colossian slave is a remarkable evidence of the freedom of access to the prisoner which was granted to all, and 'a beautiful illustration both of the character of St. Paul and the transfiguring power and righteous principles of the gospel.'"

Onesimus is the title of a platform computer game published by Ark Multimedia Publishing in 1992.