Pronunciation: (pas'turn),[key] —n. 1. the part of the foot of a horse, cow, etc., between the fetlock and the hoof. See diag. under horse. 2. either of the two bones of this part, the upper or first phalanx (great pastern bone) and the lower or second phalanx (small pastern bone), between which is a joint (pas'tern joint").