The words trade, trayed sound the same but have different meanings and spellings. Why do trade, trayed sound the same even though they are completely different words?
The answer is simple: trade, trayed are homophones of the English language.
The business of buying and selling commodities; commerce. See Synonyms at business.
The people working in or associated with a business or industry: a textile-exporting publication for the trade.
The customers of a specified business or industry; clientele.
The act or an instance of buying or selling; transaction.
Simple past tense and past participle of tray.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, 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.
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").