gravel vs bank gravel

gravel and bank gravel both are nouns.

Word	Noun	Adjective	Verb	Adverb
gravel	Yes	No	Yes	No
bank gravel	Yes	No	No	No

As nouns, bank gravel is a hyponym of gravel; that is, bank gravel is a word with a more specific, narrower meaning than gravel:

Other hyponyms of gravel include ballast, pit-run gravel, pit run, shingle.

gravel (noun)	bank gravel (noun)
rock fragments and pebbles	gravel as found in natural deposits

gravel (verb)	bank gravel (verb)
be a mystery or bewildering to
cover with gravel
cause annoyance in; disturb, especially by minor irritations