/im pak"sheuhn/ , n.
1. an act or instance of impacting.
2. the state of being impacted; close fixation.
3. Dentistry. the condition in which a tooth is impacted.
[ 1730-40; impaction- (s. of impactio ), equiv. to L impact ( us ), ptp. of impingere (see IMPACTED) + -ion- -ION ]