endocytosisPronunciation: /ˌɛndəʊsʌɪˈtəʊsɪs/Definition of endocytosis noun [mass noun] Biology the taking in of matter by a living cell by invagination of its membrane to form a vacuole. Derivatives endocytoticPronunciation: /-sʌɪˈtɒtɪk/ adjective endocytosis in other Oxford dictionaries Definition of endocytosis in the US English dictionary