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.
tie the knot Slang To perform a marriage ceremony.
tie the knot Slang To get married.
tie one on Slang To become intoxicated; go on a drinking spree.
tie up To place (funds) so as to make inaccessible for other uses: tied up her cash in long-term investments.
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.