1530s, "secret, not divulged," from L. occultus "hidden, concealed, secret," pp. of occulere "cover over, conceal," from ob "over" + a verb related to celare "to hide," from PIE base *kel- (see cell). 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.