fill up vs eat

fill up and eat both are verbs.

Word	Noun	Adjective	Verb	Adverb
fill up	No	No	Yes	No
eat	No	No	Yes	No

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

fill up (verb)	eat (verb)
make full, also in a metaphorical sense	cause to deteriorate due to the action of water, air, or an acid
become full	take in solid food
eat until one is sated	eat a meal; take a meal
fill or stop up	take in food; used of animals only
	use up (resources or materials)
	worry or cause anxiety in a persistent way