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.
Derivatives:
expertly adv. expertness n.
Etymology: ME f. OF f. L expertus past part. of experiri: see EXPERIENCE