A.T. Robertson Commentary John 20:24

"But Thomas, one of the twelve, called Didymus, was not with them when Jesus came." — John 20:24 (ASV)

Didymus (Διδυμος). The same expression applied to Thomas in 11:16; 21:2, but nowhere else in N.T. Old word for twin (double), "the pessimist of the apostolic band" (Bernard). The term twelve is still applied to the group, though Judas, the traitor, is dead.