The words beaut, butte sound the same but have different meanings and spellings. Why do beaut, butte sound the same even though they are completely different words?
The answer is simple: beaut, butte are homophones of the English language.
Slang Something outstanding of its kind: "When I make a mistake, it's a beaut!” ( Fiorello H. La Guardia).
Chiefly Western U.S. A hill that rises abruptly from the surrounding area and has sloping sides and a flat top.
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").