The words rung, wrung sound the same but have different meanings and spellings. Why do rung, wrung sound the same even though they are completely different words?
The answer is simple: rung, wrung are homophones of the English language.
A rod or bar forming a step of a ladder.
A crosspiece between the legs of a chair.
The spoke in a wheel.
Nautical One of the spokes or handles on a ship's wheel.
Past tense and past participle of wring.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition 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").