leftovers vs food

leftovers and food both are nouns.

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

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

leftovers: food remaining from a previous meal
food: any solid substance (as opposed to liquid) that is used as a source of nourishment

Other hypernyms of leftovers include solid food.

leftovers (noun)	food (noun)
food remaining from a previous meal	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