The words slaying, sleighing sound the same but have different meanings and spellings. Why do slaying, sleighing sound the same even though they are completely different words?
The answer is simple: slaying, sleighing are homophones of the English language.
Killing, especially murder of a human.
Present participle of slay.
Present participle of sleigh.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.