The words knave, nave sound the same but have different meanings and spellings. Why do knave, nave sound the same even though they are completely different words?
The answer is simple: knave, nave are homophones of the English language.
An unprincipled, crafty fellow.
A male servant.
A man of humble birth.
Games See jack.
The central part of a church, extending from the narthex to the chancel and flanked by aisles.
The hub of a wheel.
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").