The words guide, guyed sound the same but have different meanings and spellings. Why do guide, guyed sound the same even though they are completely different words?
The answer is simple: guide, guyed are homophones of the English language.
One who shows the way by leading, directing, or advising.
One who serves as a model for others, as in a course of conduct.
A person employed to conduct others, as through a museum, and give information about points of interest encountered.
Something, such as a pamphlet, that offers basic information or instruction: a shopper's guide.
Fitted with or attached to a guy.
Fitted to serve as a guy.
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").