The words one, won sound the same but have different meanings and spellings. Why do one, won sound the same even though they are completely different words?
The answer is simple: one, won are homophones of the English language.
Being a single entity, unit, object, or living being.
Characterized by unity; undivided: They spoke with one voice.
Of the same kind or quality: two animals of one species.
Forming a single entity of two or more components: three chemicals combining into one solution.
Archaic To dwell or abide.
See Table at currency.
Past tense and past participle of win.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").