(1):
(n.) The driving of one fragment of bone into another so that the fragments are not movable upon each other; as, impaction of the skull or of the hip.
(2):
(n.) An immovable packing; (Med.), a lodgment of something in a strait or passage of the body; as, impaction of the fetal head in the strait of the pelvis; impaction of food or feces in the intestines of man or beast.