adj. & n.
adj. 1 (often foll. by at, in) having special knowledge or skill in a subject. 2 involving or resulting from this (expert evidence; an expert piece of work).
n. (often foll. by at, in) a person having special knowledge or skill. expertly adv. expertness n.
[ ME f. OF f. L expertus past part. of experiri: see EXPERIENCE ]