1655-65; < Medieval Latinadeptus one who has attained (the secret of transmuting metals), noun use of L past participle of adipiscī to attain to (ad-ad- + -ep-, combining form of ap- in aptusapt + -tus past participle suffix)
1690s, "completely skilled" from Latin adeptus "having reached, attained," past participle of adipisci "to come up with, arrive at," figuratively "to attain to, acquire," from ad- "to" (see ad-) + apisci "grasp, attain," related to aptus "fitted" (see apt). Related: Adeptly.
"an expert," especially "one who is skilled in the secrets of anything," 1660s, from Latin adeptus (see adept (adj.)). The Latin adjective was used as a noun in this sense in Medieval Latin among alchemists.