loon / lune 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. 👇
loon: (noun) a worthless lazy fellow. (noun) large somewhat primitive fish-eating diving bird of the northern hemisphere having webbed feet placed far back; related to the grebes.
lune: NA
loon: l·UW·n
lune: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)