n. & v.
n. 1 (often foll. by on, against) the action of one body coming forcibly into contact with another. 2 an effect or influence, esp. when strong.
v.tr. 1 (often foll. by in, into) press or fix firmly. 2 (as impacted adj.) a (of a tooth) wedged between another tooth and the jaw. b (of a fractured bone) with the parts crushed together. c (of faeces) lodged in the intestine. impaction n.
[ L impact- part. stem of impingere IMPINGE ]