not knowable; incapable of being known or understood.
–noun
2.
something that is unknowable.
3.
the Unknowable, the postulated reality lying behind all phenomena but not cognizable by any of the processes by which the mind cognizes phenomenal objects.
un·know·a·ble (ŭn-nō'ə-bəl) adj. Impossible to know, especially being beyond the range of human experience or understanding: the unknowable mysteries of life. un·know'a·bil'i·ty, un·know'a·ble·ness n., un·know'a·ble n., un·know'a·bly adv.