The words draft, draught sound the same but have different meanings and spellings. Why do draft, draught sound the same even though they are completely different words?
The answer is simple: draft, draught are homophones of the English language.
A current of air in an enclosed area.
A device that regulates the flow or circulation of air.
The act of pulling loads; traction.
Something that is pulled or drawn; a load.
Chiefly British Variant of draft.
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").