barrel vs beer barrel

barrel and beer barrel both are nouns.

Word	Noun	Adjective	Verb	Adverb
barrel	Yes	No	Yes	No
beer barrel	Yes	No	No	No

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

Other hyponyms of barrel include beer keg, butt, hogshead, keg, pickle barrel, shook, tun, wine barrel, wine cask.

barrel (noun)	beer barrel (noun)
a cylindrical container that holds liquids	a barrel that holds beer
a tube through which a bullet travels when a gun is fired
any of various units of capacity
the quantity that a barrel (of any size) will hold
a bulging cylindrical shape; hollow with flat ends

barrel (verb)	beer barrel (verb)
put in barrels