The words rise, ryes, ryse sound the same but have different meanings and spellings. Why do rise, ryes, ryse sound the same even though they are completely different words?
The answer is simple: rise, ryes, ryse are homophones of the English language.
To assume a standing position after lying, sitting, or kneeling.
To get out of bed: rose at dawn.
To move from a lower to a higher position; ascend: Hot air rises.
To increase in size, volume, or level: The river rises every spring.
Plural form of rye.
A Middle English form of rise, rise.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License, from The Century Dictionary and Cyclopedia 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").