berth vs lower berth

berth and lower berth both are nouns.

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

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

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

berth (noun)	lower berth (noun)
a job in an organization	the lower of two berths
a bed on a ship or train; usually in tiers
a place where a craft can be made fast

berth (verb)	lower berth (verb)
secure in or as if in a berth or dock
come into or dock at a wharf
provide with a berth