blah vs rhetoric

blah and rhetoric both are nouns.

Word	Noun	Adjective	Verb	Adverb
blah	Yes	No	No	No
rhetoric	Yes	No	No	No

As nouns, rhetoric is a hypernym of blah; that is, rhetoric is a word with a broader meaning than blah:

Other hypernyms of blah include grandiloquence, grandiosity, magniloquence, ornateness.

blah (noun)	rhetoric (noun)
pompous or pretentious talk or writing	study of the technique and rules for using language effectively (especially in public speaking)
	using language effectively to please or persuade
	high-flown style; excessive use of verbal ornamentation
	loud and confused and empty talk