fast food vs nourishment

fast food and nourishment both are nouns.

Word	Noun	Adjective	Verb	Adverb
fast food	Yes	No	No	No
nourishment	Yes	No	No	No

As nouns, nourishment is a hypernym of fast food; that is, nourishment is a word with a broader meaning than fast food:

fast food: inexpensive food (hamburgers or chicken or milkshakes) prepared and served quickly
nourishment: a source of materials to nourish the body

Other hypernyms of fast food include aliment, alimentation, nutriment, nutrition, sustenance, victuals.

fast food (noun)	nourishment (noun)
inexpensive food (hamburgers or chicken or milkshakes) prepared and served quickly	the act of nourishing
	a source of materials to nourish the body