pillow vs cushion

pillow and cushion both are nouns.

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

As nouns, cushion is a hypernym of pillow; that is, cushion is a word with a broader meaning than pillow:

pillow: a cushion to support the head of a sleeping person
cushion: a soft bag filled with air or a mass of padding such as feathers or foam rubber etc.

pillow (noun)	cushion (noun)
a cushion to support the head of a sleeping person	a soft bag filled with air or a mass of padding such as feathers or foam rubber etc.
	a mechanical damper; absorbs energy of sudden impulses
	the layer of air that supports a hovercraft or similar vehicle

pillow (verb)	cushion (verb)
rest on or as if on a pillow	protect from impact