stereoisomer Syllabification: (ster·e·o·i·so·mer)Pronunciation: /ˌsterē-ōˈīsəmər, ˌsti(ə)r-/Definition of stereoisomer noun Chemistry each of two or more compounds differing only in the spatial arrangement of their atoms. Derivatives stereoisomericPronunciation: /-ˌīsəˈmerik/ adjective stereoisomerismPronunciation: /-īˈsäməˌrizəm/ noun stereoisomer in other Oxford dictionaries Definition of stereoisomer in the British & World English dictionary