howler vs foul-up

howler and foul-up both are nouns.

Word	Noun	Adjective	Verb	Adverb
howler	Yes	No	No	No
foul-up	Yes	No	No	No

As nouns, foul-up is a hypernym of howler; that is, foul-up is a word with a broader meaning than howler:

Other hypernyms of howler include bloomer, blooper, blunder, boner, boo-boo, botch, bungle, flub, fuckup, pratfall.

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