breakfast vs eat

breakfast is a noun but eat is not a noun.

Word	Noun	Adjective	Verb	Adverb
breakfast	Yes	No	Yes	No
eat	No	No	Yes	No

As verbs, eat is a hypernym of breakfast; that is, eat is a word with a broader meaning than breakfast:

breakfast (noun)	eat (noun)
the first meal of the day (usually in the morning)

breakfast (verb)	eat (verb)
eat an early morning meal	cause to deteriorate due to the action of water, air, or an acid
provide breakfast for	take in solid food
	eat a meal; take a meal
	take in food; used of animals only
	use up (resources or materials)
	worry or cause anxiety in a persistent way