The words baroness, barrenness sound the same but have different meanings and spellings. Why do baroness, barrenness sound the same even though they are completely different words?
The answer is simple: baroness, barrenness are homophones of the English language.
Used as the title for such a noblewoman.
A woman holding the title to a barony.
The wife or widow of a baron.
The property of being barren; the property of not supporting life.
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.