The words pained, paned sound the same but have different meanings and spellings. Why do pained, paned sound the same even though they are completely different words?
The answer is simple: pained, paned are homophones of the English language.
Simple past tense and past participle of pain.
In pain, especially in an emotional sense.
Having a specified kind or number of panes. Often used in combination: clear-paned windows; double-paned French doors.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, 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").