The words toon, tune sound the same but have different meanings and spellings. Why do toon, tune sound the same even though they are completely different words?
The answer is simple: toon, tune are homophones of the English language.
A tall tree (Cedrela toona) of tropical Asia and Australia, having dark red, aromatic wood.
The wood of this tree.
Informal A cartoon, especially an animated cartoon.
Informal A character in an animated cartoon.
To adopt or adjust, especially in order to bring into harmony.
Music A melody, especially a simple and easily remembered one.
Music A song.
Music Correct pitch.
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.