junk food vs food

junk food and food both are nouns.

Word	Noun	Adjective	Verb	Adverb
junk food	Yes	No	No	No
food	Yes	No	No	No

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

junk food: food that tastes good but is high in calories having little nutritional value
food: any solid substance (as opposed to liquid) that is used as a source of nourishment

Other hypernyms of junk food include solid food.

junk food (noun)	food (noun)
food that tastes good but is high in calories having little nutritional value	any substance that can be metabolized by an animal to give energy and build tissue
	anything that provides mental stimulus for thinking
	any solid substance (as opposed to liquid) that is used as a source of nourishment