fissure

noun

1. 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.”

2. A groove, deep furrow, elongated cleft or tear between body parts or in the substance of an organ.
3. A break or slit in tissue usually at the junction of skin and mucous membrane.
4. A state of incompatibility or disagreement.

verb

1. To split, forming fissures.