What is the X in X-mas?
1650s, Modern Latin, from Greek metakarpion, from meta- (see meta-) + karpos "wrist" (see carpus). Related: Metacarpal.
metacarpus met·a·car·pus (mět'ə-kär'pəs)n. pl. met·a·car·pi (-pī) The part of the hand that includes the five bones between the fingers and the wrist.