The words rabbet, rabbit sound the same but have different meanings and spellings. Why do rabbet, rabbit sound the same even though they are completely different words?
The answer is simple: rabbet, rabbit are homophones of the English language.
A cut or groove along or near the edge of a piece of wood that allows another piece to fit into it to form a joint.
A joint so made.
To cut a rabbet in.
To join by a rabbet.
Any of various long-eared, short-tailed, burrowing mammals of the family Leporidae, as the commonly domesticated Old World species Oryctolagus cuniculus or the cottontail.
The fur of a rabbit or hare.
Sports A runner who intentionally sets a fast pace for a teammate during a long-distance race.
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").