a Judas kiss

a Judas kiss

an act of betrayal, especially one disguised as a gesture of friendship.
Judas Iscariot was the disciple who betrayed Jesus to the authorities in return for thirty pieces of silver: ‘And he that betrayed him gave them a sign, saying, Whomsoever I shall kiss, that same is he: hold him fast’ (Matthew 26:48).
See also: Judas, kiss