foul / fowl 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. 👇
foul: (noun) an act that violates the rules of a sport. (verb) hit a foul ball. (verb) commit a foul; break the rules. (verb) spot, stain, or pollute. (verb) make unclean. (verb) become soiled and dirty. (adjective) (of a baseball) not hit between the foul lines.
fowl: (verb) hunt fowl. (verb) hunt fowl in the forest.
foul: f·AW·l
fowl: f·AW·l
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)