Entry 2 senses Webster, 1913 Polymorphism /päl-ē-môrʹfĭz-əm/ · Pol·y·mor·phism · IPA /pɑliˈmɔɹfɪz(ə)m/ 01 n. Same as Pleomorphism. 1. Same as Pleomorphism.(Crystallog.) See: Pleomorphism 2. The capability of assuming different forms; the capability of widely varying in form.(Biol.)