fisher / fissure are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
fisher: (noun) large dark brown North American arboreal carnivorous mammal.
fissure: (noun) (anatomy) a long narrow slit or groove that divides an organ into lobes. (verb) break into fissures or fine cracks.
fisher: f·IH·sh·er
fissure: f·IH·sh·er
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)