biosynthesis Syllabification: (bi·o·syn·the·sis)Pronunciation: /ˌbīōˈsinTHəsis/Definition of biosynthesis noun the production of complex molecules within living organisms or cells. Derivatives biosyntheticPronunciation: /-ˌsinˈTHetik/ adjective biosynthesis in other Oxford dictionaries Definition of biosynthesis in the British & World English dictionary