The words crappie, crappy sound the same but have different meanings and spellings. Why do crappie, crappy sound the same even though they are completely different words?
The answer is simple: crappie, crappy are homophones of the English language.
Either of two edible North American sunfishes, the black crappie (Pomoxis nigromaculatus) or the white crappie (P. annularis).
Vulgar Slang Inferior; worthless.
Vulgar Slang Miserable; wretched.
Vulgar Slang Mean; contemptible.
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").