The words bus, buss sound the same but have different meanings and spellings. Why do bus, buss sound the same even though they are completely different words?
The answer is simple: bus, buss are homophones of the English language.
A long motor vehicle for carrying passengers, usually along a fixed route.
Informal A large or ungainly automobile.
A four-wheeled cart for carrying dishes in a restaurant.
Electricity A bus bar.
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").