Noumenon

‖n. [ NL. fr. Gr. &unr_; the thing perceived, p. pr. pass. of &unr_; to perceive, &unr_; the mind. ] (Metaph.) The of itself unknown and unknowable rational object, or thing in itself, which is distinguished from the phenomenon through which it is apprehended by the senses, and by which it is interpreted and understood; -- so used in the philosophy of Kant and his followers. [ 1913 Webster ]