pleomorphismPronunciation: /ˌpliːə(ʊ)ˈmɔːfɪz(ə)m/Definition of pleomorphism noun [mass noun] the occurrence of more than one distinct form of a natural object, such as a crystalline substance, a virus, the cells in a tumour, or an organism at different stages of the life cycle. Derivatives pleomorphic adjective Origin: mid 19th century: from Greek pleiōn 'more' + morphē 'form' + -ismpleomorphism in other Oxford dictionaries Definition of pleomorphism in the US English dictionary