fissure

Short definition from Wiktionary

Noun

1. 1
   A long, narrow crack or opening made by breaking or splitting, especially in rock or earth.
2. 2
   A groove, deep furrow, elongated cleft or tear between body parts or in the substance of an organ.
3. 3
   A break or slit in tissue usually at the junction of skin and mucous membrane.
4. 4
   A state of incompatibility or disagreement.

Verb

1. 1
   To split, forming fissures.