fissure UK /ˈfɪʃ.ə/US /ˈfɪʃ.ɚ/noun 4verb 1forms 3 noun4 •A long, narrow crack or opening made by breaking or splitting, especially in rock or earth.After Miller's Dale Junction, the main Derby-Manchester line crosses the Wye for the last time and turns north-west up Great Rocks Dale, a natural fissure several miles long. — 1960 •A groove, deep furrow, elongated cleft or tear between body parts or in the substance of an organ. •A break or slit in tissue usually at the junction of skin and mucous membrane. •A state of incompatibility or disagreement. verb1 •To split, forming fissures. formsfissured · fissuring · fissures