beer keg vs beer barrel

beer keg and beer barrel both are nouns.

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

As nouns, beer keg and beer barrel are synonyms defined as:

beer keg (noun)	beer barrel (noun)
a barrel that holds beer	a barrel that holds beer