cask vs tun

cask and tun both are nouns.

Word	Noun	Adjective	Verb	Adverb
cask	Yes	No	No	No
tun	Yes	No	No	No

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

cask: a cylindrical container that holds liquids
tun: a large cask especially one holding a volume equivalent to 2 butts or 252 gals

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

cask (noun)	tun (noun)
a cylindrical container that holds liquids	a large cask especially one holding a volume equivalent to 2 butts or 252 gals
the quantity a cask will hold