biosynthesisPronunciation: /bʌɪə(ʊ)ˈsɪnθɪsɪs/Definition of biosynthesis noun [mass noun] the production of complex molecules within living organisms or cells. Derivatives biosyntheticPronunciation: /-ˈθɛtɪk/ adjective biosynthesis in other Oxford dictionaries Definition of biosynthesis in the US English dictionary