boy / buoy 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. 👇
boy: (noun) a friendly informal reference to a grown man. (noun) (ethnic slur) offensive and disparaging term for Black man.
buoy: (noun) bright-colored; a float attached by rope to the seabed to mark channels in a harbor or underwater hazards. (verb) float on the surface of water. (verb) keep afloat. (verb) mark with a buoy.
boy: b·OY
buoy: b·UW·iy
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)