let slip from memory (verb) forget: not be able to remember
Sinonime: Delphic,
arcane, baffling, cabalistic,
dark,
enigmatic, enigmatical,
hidden, incognizable, indiscernible,
inexplicable,
inscrutable, mysterious, mystic,
obscure, sibylline, unaccountable,
unfathomable, ungraspable, unintelligible, unknowable
Antonime: comprehensible,
intelligible, penetrable,
understandable