lower berth vs bunk

lower berth and bunk both are nouns.

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

As nouns, bunk is a hypernym of lower berth; that is, bunk is a word with a broader meaning than lower berth:

Other hypernyms of lower berth include berth, built in bed.

lower berth (noun)	bunk (noun)
the lower of two berths	a bed on a ship or train; usually in tiers
	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

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