blunder vs howler

blunder and howler both are nouns.

Word	Noun	Adjective	Verb	Adverb
blunder	Yes	No	Yes	No
howler	Yes	No	No	No

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

blunder (noun)	howler (noun)
an embarrassing mistake	a glaring blunder
	monkey of tropical South American forests having a loud howling cry
	a joke that seems extremely funny

blunder (verb)	howler (verb)
utter impulsively
make one's way clumsily or blindly
commit a faux pas or a fault or make a serious mistake