fin / finn 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. 👇
fin: (noun) a stabilizer on a ship that resembles the fin of a fish. (noun) organ of locomotion and balance in fishes and some other aquatic animals. (verb) equip (a car) with fins. (verb) propel oneself through the water in a finning motion. (verb) show the fins above the water while swimming.
finn: (noun) a native or inhabitant of Finland.
fin: f·IH·n
finn: f·IH·n
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)