dullard vs windbag

dullard and windbag both are nouns.

Word	Noun	Adjective	Verb	Adverb
dullard	Yes	No	No	No
windbag	Yes	No	No	No

As nouns, windbag is a hyponym of dullard; that is, windbag is a word with a more specific, narrower meaning than dullard:

Other hyponyms of dullard include gasbag, nudnick, nudnik, platitudinarian, stuffed shirt.

dullard (noun)	windbag (noun)
a person who evokes boredom	a boring person who talks a great deal about uninteresting topics
a person who is not very bright