bum vs scum bag

bum and scum bag both are nouns.

Word	Noun	Adjective	Verb	Adverb
bum	Yes	Yes	Yes	No
scum bag	Yes	No	No	No

As nouns, bum and scum bag are synonyms defined as:

bum and scum bag: a person who is deemed to be despicable or contemptible

Other synonyms of bum include crumb, dirty dog, git, lowlife, puke, rat, rotter, scumbag, skunk, so-and-so, stinker, stinkpot.

bum (noun)	scum bag (noun)
the fleshy part of the human body that you sit on	a person who is deemed to be despicable or contemptible
a vagrant
a person who is deemed to be despicable or contemptible
person who does no work

bum (adjective)	scum bag (adjective)
of very poor quality; flimsy

bum (verb)	scum bag (verb)
ask for and get free; be a parasite
be lazy or idle