occult

occult blood loss; occult cancer

Be aware that occult knowledge can be used for good or evil purposes.

Elbows almost touching they leaned at ease, idly reading the almost obliterated lines engraved there. ¶ "I never understood it," she observed, lightly scornful. "What occult meaning has a sun-dial for the spooney? I'm sure I don't want to read riddles in a strange gentleman's optics."