The words kneaded, needed sound the same but have different meanings and spellings. Why do kneaded, needed sound the same even though they are completely different words?
The answer is simple: kneaded, needed are homophones of the English language.
Simple past tense and past participle of knead.
Simple past tense and past participle of need.
Necessary; being needed.
Definitions 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.