microsome Syllabification: (mi·cro·some)Pronunciation: /ˈmīkrəˌsōm/Definition of microsome noun Biology a fragment of endoplasmic reticulum and attached ribosomes obtained by the centrifugation of homogenized cells. Derivatives microsomalPronunciation: /ˌmīkrəˈsōməl/ adjective microsome in other Oxford dictionaries Definition of microsome in the British & World English dictionary