smorgasbord vs grab bag

smorgasbord and grab bag both are nouns.

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

As nouns, grab bag is a hyponym of smorgasbord; that is, grab bag is a word with a more specific, narrower meaning than smorgasbord:

smorgasbord (noun)	grab bag (noun)
an assortment of foods starting with herring or smoked eel or salmon etc with bread and butter; then cheeses and eggs and pickled vegetables and aspics; finally hot foods; served as a buffet meal	a container from which a person draws a wrapped item at random without knowing the contents
a collection containing a variety of sorts of things	an assortment of miscellaneous items