microfilament Syllabification: (mi·cro·fil·a·ment)Pronunciation: /ˌmīkrōˈfiləmənt/Definition of microfilament noun Biology a small rodlike structure, about 4-7 nanometers in diameter, present in numbers in the cytoplasm of many eukaryotic cells. microfilament in other Oxford dictionaries Definition of microfilament in the British & World English dictionary