enallage

‖n. [ L., fr. Gr. &unr_; an exchange, fr. &unr_; to exchange; &unr_; in + &unr_; to change. ] (Gram.) A substitution, as of one part of speech for another, of one gender, number, case, person, tense, mode, or voice, of the same word, for another. [ 1913 Webster ]