The words halve, have sound the same but have different meanings and spellings. Why do halve, have sound the same even though they are completely different words?
The answer is simple: halve, have are homophones of the English language.
To lessen or reduce by half: halved the recipe to serve two.
To divide (something) into two equal portions or parts.
Informal To share (something) equally: The twins halve everything.
Sports To play (a golf game or hole) using the same number of strokes as one's opponent.
have at To attack.
have on To wear: had on red shoes.
To be in possession of: already had a car.
To possess as a characteristic, quality, or function: has a beard; had a great deal of energy.
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.