microfibril Syllabification: (mi·cro·fi·bril)Pronunciation: /ˌmīkrōˈfībrəl, -ˈfibrəl/Definition of microfibril noun Biology a small fibril in the cytoplasm or wall of a cell, visible only under an electron microscope, and typically aggregated into coarser fibrils or structures. microfibril in other Oxford dictionaries Definition of microfibril in the British & World English dictionary