firkin vs British capacity unit

firkin and British capacity unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
firkin	Yes	No	No	No
British capacity unit	Yes	No	No	No

As nouns, British capacity unit is a hypernym of firkin; that is, British capacity unit is a word with a broader meaning than firkin:

firkin: a British unit of capacity equal to 9 imperial gallons
British capacity unit: a unit of measure for capacity officially adopted in the British Imperial System; British units are both dry and wet

Other hypernyms of firkin include Imperial capacity unit.

firkin (noun)	British capacity unit (noun)
a small wooden keg	a unit of measure for capacity officially adopted in the British Imperial System; British units are both dry and wet
a British unit of capacity equal to 9 imperial gallons