built in bed vs upper

built in bed and upper both are nouns.

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

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

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

built in bed (noun)	upper (noun)
a bed on a ship or train; usually in tiers	piece of leather or synthetic material that forms the part of a shoe or boot above the sole that encases the foot
	a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression
	the higher of two berths

built in bed (adjective)	upper (adjective)
	the topmost one of two; upper
	higher in place or position
	superior in rank or accomplishment