pillow vs bed pillow

pillow and bed pillow both are nouns.

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

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

Other hyponyms of pillow include bolster, long pillow.

pillow (noun)	bed pillow (noun)
a cushion to support the head of a sleeping person	a soft pillow for use on a bed

pillow (verb)	bed pillow (verb)
rest on or as if on a pillow