/im pak"tid/ , adj.
1. tightly or immovably wedged in.
2. Dentistry. noting a tooth so confined in its socket as to be incapable of normal eruption.
3. driven together; tightly packed.
4. densely populated or crowded; overcrowded: an impacted school district.
[ 1675-85; obs. impact adj. ( impactus ptp. of impingere to fasten, cause to collide, strike, equiv. to im- IM- 1 + pag-, var. s. of pangere to drive in, plant firmly + -tus ptp. suffix) + -ED 2 ; see IMPINGE ]