linen vs bed linen

linen and bed linen both are nouns.

Word	Noun	Adjective	Verb	Adverb
linen	Yes	No	No	No
bed linen	Yes	No	No	No

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

Other hyponyms of linen include bath linen, doily, doyley, doyly, napery, table linen.

linen (noun)	bed linen (noun)
white goods or clothing made with linen cloth	linen or cotton articles for a bed (as sheets and pillowcases)
a fabric woven with fibers from the flax plant
a high-quality paper made of linen fibers or with a linen finish