The words narc, nark sound the same but have different meanings and spellings. Why do narc, nark sound the same even though they are completely different words?
The answer is simple: narc, nark are homophones of the English language.
Slang A law enforcement officer who deals with narcotics violations.
Slang Variant of narc.
An informer, especially a police informer.
To be an informer.
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.