noun

1. a long, narrow, deep cleft or crack
2. a dividing or breaking into parts
3. Anat. a groove between lobes or parts of an organ, as in the brain
4. Med. a break or ulceration where skin and mucous membrane join anal fissure

Etymology: ME < OFr < L fissura < fissus: see fission

transitive verb, intransitive verb fissured -·sured, fissuring -·sur·ing