polyptoton

‖n. [ L., fr. Gr. &unr_; having, or being in, many cases; poly`s many + &unr_; case. ] (Rhet.) A figure by which a word is repeated in different forms, cases, numbers, genders, etc., as in Tennyson's line, -- “My own heart's heart, and ownest own, farewell.” [ 1913 Webster ]