The words gunnel, gunwhale sound the same but have different meanings and spellings. Why do gunnel, gunwhale sound the same even though they are completely different words?
The answer is simple: gunnel, gunwhale are homophones of the English language.
Any of various small, elongated fishes of the family Pholidae, common in the tidal pools and coastal waters of northern seas.
Variant of gunwale.
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").