1530s, "secret, not divulged," from Middle French occulte and directly from Latin occultus "hidden, concealed, secret," past participle of occulere "cover over, conceal," from assimilated form of ob "over" (see ob-) + a verb related to celare "to hide," from PIE root *kel- (1) "to cover, conceal, save." Meaning "not apprehended by the mind, beyond the range of understanding" is from 1540s. The association with the supernatural sciences (magic, alchemy, astrology, etc.) dates from 1630s.
