The words riot, ryot sound the same but have different meanings and spellings. Why do riot, ryot sound the same even though they are completely different words?
The answer is simple: riot, ryot are homophones of the English language.
A wild or turbulent disturbance created by a large number of people.
Law A violent disturbance of the public peace by three or more persons assembled for a common purpose.
An unrestrained outbreak, as of laughter or passions.
A profusion: The garden was a riot of colors in August.
A farmer or tiller of the soil.
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").