grab bag vs assortment

grab bag and assortment both are nouns.

Word	Noun	Adjective	Verb	Adverb
grab bag	Yes	No	No	No
assortment	Yes	No	No	No

As nouns, assortment is a hypernym of grab bag; that is, assortment is a word with a broader meaning than grab bag:

Other hypernyms of grab bag include miscellanea, miscellany, mixed bag, mixture, motley, potpourri, salmagundi, smorgasbord, variety.

grab bag (noun)	assortment (noun)
a container from which a person draws a wrapped item at random without knowing the contents	the act of distributing things into classes or categories of the same type
an assortment of miscellaneous items	a collection containing a variety of sorts of things