New Testament name, borne by one of Christ's twelve apostles, referred to as ‘Thomas, called Didymus’ (John 11:16; 20:24). Didymos is the Greek word for ‘twin’, and the name is the Greek form of an Aramaic byname meaning ‘twin’. The given name has always been popular throughout Christendom, in part because St Thomas's doubts have made him seem a very human character.
Irish: reduced form of O’Hayden, an Anglicized form of Gaelic Ó hÉideáin and Ó hÉidín ‘descendant of Éideán’ or ‘descendant of Éidín’, personal names apparently from a diminutive of éideadh ‘clothes’, ‘armor’. There was also a Norman family bearing the English name (see 2 below), living in County Wexford.