sad sack vs blunderer

sad sack and blunderer both are nouns.

Word	Noun	Adjective	Verb	Adverb
sad sack	Yes	No	No	No
blunderer	Yes	No	No	No

As nouns, sad sack and blunderer are synonyms defined as:

sad sack and blunderer: someone who makes mistakes because of incompetence

Other synonyms of sad sack include botcher, bumbler, bungler, butcher, fuckup, fumbler, stumbler.

sad sack (noun)	blunderer (noun)
someone who makes mistakes because of incompetence	someone who makes mistakes because of incompetence