The words born, bourn, bourne sound the same but have different meanings and spellings. Why do born, bourn, bourne sound the same even though they are completely different words?
The answer is simple: born, bourn, bourne are homophones of the English language.
A past participle of bear1.
Brought into life by birth.
Brought into existence; created: A new nation was born with the revolution.
Having from birth a particular quality or talent: a born artist.
A small stream; a brook.
Archaic A destination; a goal.
Archaic A boundary; a limit.
A goal or destination.
A stream or brook in which water flows only seasonally.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, 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.