barrel vs pickle barrel

barrel and pickle barrel both are nouns.

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

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

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

barrel (noun)	pickle barrel (noun)
a cylindrical container that holds liquids	a barrel holding vinegar in which cucumbers are pickled
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)	pickle barrel (verb)
put in barrels