built in bed vs lower

built in bed and lower both are nouns.

Word	Noun	Adjective	Verb	Adverb
built in bed	Yes	No	No	No
lower	Yes	Yes	Yes	No

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

Other hyponyms of built in bed include lower berth, upper, upper berth, couchette.

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

built in bed (adjective)	lower (adjective)
	the bottom one of two

built in bed (verb)	lower (verb)
	make lower or quieter
	set lower
	cause to drop or sink
	move something or somebody to a lower position
	look angry or sullen, wrinkle one's forehead, as if to signal disapproval