microfilamentPronunciation: /ˈmʌɪkrə(ʊ)ˌfɪləm(ə)nt/Definition of microfilament noun Biology a small rod-like structure, about 4-7 nanometres in diameter, present in numbers in the cytoplasm of many eukaryotic cells. microfilament in other Oxford dictionaries Definition of microfilament in the US English dictionary