The words tie, tye sound the same but have different meanings and spellings. Why do tie, tye sound the same even though they are completely different words?
The answer is simple: tie, tye are homophones of the English language.
To fasten or secure with or as if with a cord, rope, or strap: tied the kite to a post; tie up a bundle.
To fasten by drawing together the parts or sides and knotting with strings or laces: tied her shoes.
To make by fastening ends or parts: tie a knot.
To put a knot or bow in: tie a neck scarf.
a knot
a patch of common land, often a village green.
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").