bunk vs upper berth

bunk and upper berth both are nouns.

Word	Noun	Adjective	Verb	Adverb
bunk	Yes	No	Yes	No
upper berth	Yes	No	No	No

As nouns, upper berth is a hyponym of bunk; that is, upper berth is a word with a more specific, narrower meaning than bunk:

Other hyponyms of bunk include lower, lower berth, upper, couchette.

bunk (noun)	upper berth (noun)
a bed on a ship or train; usually in tiers	the higher of two berths
a rough bed (as at a campsite)
beds built one above the other
a long trough for feeding cattle
unacceptable behavior (especially ludicrously false statements)
a message that seems to convey no meaning

bunk (verb)	upper berth (verb)
flee; take to one's heels; cut and run
provide with a bunk
avoid paying