breakfast food vs solid food

breakfast food and solid food both are nouns.

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

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

breakfast food: any food (especially cereal) usually served for breakfast
solid food: any solid substance (as opposed to liquid) that is used as a source of nourishment

Other hypernyms of breakfast food include food.

breakfast food (noun)	solid food (noun)
any food (especially cereal) usually served for breakfast	any solid substance (as opposed to liquid) that is used as a source of nourishment