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 (especially Ulster): Anglicized form of the Gaelic surname Mac Cú Uladh, a patronymic from Cú Uladh ‘hound of Ulster’. Compare McNally, which is from Mac Con Uladh, genitive form of the same name. It has sometimes been erroneously associated with Gaelic cullach ‘wild boar’, and some families in County Sligo have translated it into English as Boar.