The words adulterous, adulteress sound the same but have different meanings and spellings. Why do adulterous, adulteress sound the same even though they are completely different words?
The answer is simple: adulterous, adulteress are homophones of the English language.
A woman who commits adultery. See Usage Note at -ess.
Relating to, inclined to, or marked by adultery.
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.