The words citing, sighting, siting sound the same but have different meanings and spellings. Why do citing, sighting, siting sound the same even though they are completely different words?
The answer is simple: citing, sighting, siting are homophones of the English language.
Present participle of cite.
The act of catching sight of something, especially something unusual or searched for: a sighting of a whale in the harbor; a reported sighting of a UFO.
Present participle of site.
Common misspelling of citing.
Common misspelling of sitting.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").