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 (Connacht) and Scottish: reduced Anglicized form of Gaelic Mac an Tánaiste ‘son of the tanist’. The word tanist denoted a senior and respected member of a clan who was heir presumptive to its chief. Clan leadership was not hereditary, but depended on ability.