The words chased, chaste sound the same but have different meanings and spellings. Why do chased, chaste sound the same even though they are completely different words?
The answer is simple: chased, chaste are homophones of the English language.
Simple past tense and past participle of chase.
Morally pure in thought or conduct; decent and modest.
Not having experienced sexual intercourse; virginal.
Abstaining from unlawful sexual intercourse.
Abstaining from all sexual intercourse; celibate.
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").