/ˈfiSHər/
Noun
1. A groove, natural division, deep furrow, elongated cleft, or tear in various parts of the body. (wikipedia.org)
2. Any cleft or groove, normal or otherwise, especially a deep fold in the cerebral cortex which involves the entire thickness of the brain wall. (wiktionary.org)
3. A long narrow slit or groove that divides an organ into lobes. (wordnetweb.princeton.edu)
Verb
1. Split or crack (something) to form a long narrow opening. (Google Dictionary)