The words brunet, brunette sound the same but have different meanings and spellings. Why do brunet, brunette sound the same even though they are completely different words?
The answer is simple: brunet, brunette are homophones of the English language.
Of a dark complexion or coloring.
Having dark brown or black hair or eyes.
A person with dark brown hair.
Having dark or brown hair.
A girl or woman with dark or brown hair.
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").