done / dun 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. 👇
done: (verb) get (something) done. (verb) proceed or get along. (verb) create or design, often in a certain way. (verb) carry on or function. (verb) travel or traverse (a distance). (adjective) having finished or arrived at completion. (adjective) cooked until ready to serve.
dun: (noun) horse of a dull brownish grey color. (noun) a color or pigment varying around a light grey-brown color. (verb) persistently ask for overdue payment. (verb) cure by salting. (verb) make a dun color. (adjective) of a dull greyish brown to brownish grey color.
done: d·AH·n
dun: d·AH·n
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)