The words sleighed, slayed sound the same but have different meanings and spellings. Why do sleighed, slayed sound the same even though they are completely different words?
The answer is simple: sleighed, slayed are homophones of the English language.
Simple past tense and past participle of slay.
To become overwhelmed by religious ecstasy.
Simple past tense and past 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.