The words bah, baa sound the same but have different meanings and spellings. Why do bah, baa sound the same even though they are completely different words?
The answer is simple: bah, baa are homophones of the English language.
To make a bleating sound, as a sheep or goat.
The bleat of a sheep or goat.
Used to express impatient rejection or contempt.
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.