1690s, "completely skilled, well-versed," from Latin adeptus "having reached or attained," past participle of adipisci "to come up with, arrive at," figuratively "to attain to, acquire," from ad "to" (see ad-) + apisci "to grasp, attain" (related to aptus "fitted," from PIE root *ap- (1) "to take, reach" (see apt). Related: Adeptly; adeptness.
"an expert, one who as attained knowledge," especially "one who is skilled in the secrets of an occult science," 1660s, from Latin adeptus (adj.) "having attained" (see adept (adj.)). The Latin adjective was used as a noun in this sense in Medieval Latin among alchemists. It implies natural and acquired ability, whereas expert implies more of experience and practice.