pro·fi·cient [pruh-fish-uhnt]

adjective
1. well-advanced or competent in any art, science, or subject; skilled: a proficient programmer.

noun
2. an expert.

Origin:
1580–90; < Latin prōficient- (stem of prōficiēns ) present participle of prōficere to advance, make progress, equivalent to prō- pro- + -ficere, combining form of facere to make, do. See -ent, efficient
1580s, from L. proficientem (nom. proficiens), prp. of proficere "to make progress, be useful" (see proficiency).

Related forms
pro·fi·cient·ly, adverb
pro·fi·cient·ness, noun
o·ver·pro·fi·cient, adjective
o·ver·pro·fi·cient·ly, adverb

Synonyms
1. adept, competent, experienced, accomplished, able, finished.

Antonyms
1. unskilled, inept.