occult (adj.)

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. A verb occult "to keep secret, conceal" (c.1500, from Latin occultare) is obsolete.