The words teal, teil sound the same but have different meanings and spellings. Why do teal, teil sound the same even though they are completely different words?
The answer is simple: teal, teil are homophones of the English language.
Any of several small, short-necked freshwater ducks, especially of the genus Anas, that feed on the surface of the water and often have brightly marked plumage.
A moderate or dark bluish green to greenish blue.
The lime tree, or linden.
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").