1. (Science: surgery) 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. (Science: medicine) An immovable packing;, a lodgment of something in a strait or passage of the body; as, impaction of the foetal head in the strait of the pelvis; impaction of food or feces in the intestines of man or beast.
Origin: L. Impactio a striking: cf. F. Impaction.