The words chough, chuff sound the same but have different meanings and spellings. Why do chough, chuff sound the same even though they are completely different words?
The answer is simple: chough, chuff are homophones of the English language.
A crowlike Old World bird of the genus Pyrrhocorax, especially P. pyrrhocorax, having black plumage and red legs.
A rude, insensitive person; a boor.
To produce or move with noisy puffing or explosive sounds: "Switch engines chuffed impatiently in busy rail yards” ( Robert Paul Jordan).
A noisy puffing or explosive sound, such as one made by a locomotive.
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").