The words bit, bitt sound the same but have different meanings and spellings. Why do bit, bitt sound the same even though they are completely different words?
The answer is simple: bit, bitt are homophones of the English language.
Informal An amount equal to one eighth of a dollar: two bits.
A small portion, degree, or amount: a bit of lint; a bit of luck.
A brief amount of time; a moment: Wait a bit.
A short scene or episode in a theatrical performance.
A vertical post, usually one of a pair, set on the deck of a ship and used to secure ropes or cables.
To wind (a cable) around a bitt.
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").