The words rind, rynd sound the same but have different meanings and spellings. Why do rind, rynd sound the same even though they are completely different words?
The answer is simple: rind, rynd are homophones of the English language.
A tough outer covering such as bark, the skin of some fruits, or the coating on cheese or bacon.
A piece of iron crossing the hole in the upper millstone, by which the stone is supported on the spindle.
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").