food vs solid food

food and solid food both are nouns.

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

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

food: any substance that can be metabolized by an animal to give energy and build tissue
solid food: any solid substance (as opposed to liquid) that is used as a source of nourishment

Other hypernyms of food include substance, food.

As nouns, food and solid food are synonyms defined as:

food and solid food: any solid substance (as opposed to liquid) that is used as a source of nourishment

food (noun)	solid food (noun)
any substance that can be metabolized by an animal to give energy and build tissue	any solid substance (as opposed to liquid) that is used as a source of nourishment
anything that provides mental stimulus for thinking
any solid substance (as opposed to liquid) that is used as a source of nourishment