The words pan, panne sound the same but have different meanings and spellings. Why do pan, panne sound the same even though they are completely different words?
The answer is simple: pan, panne are homophones of the English language.
A shallow, wide, open container, usually of metal and without a lid, used for holding liquids, cooking, and other domestic purposes.
A vessel similar in form to a pan, especially:
An open metal dish used to separate gold or other metal from gravel or waste by washing.
Either of the receptacles on a balance or pair of scales.
A special finish for velvet and satin that produces a high luster.
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").