eat vs fill up

eat and fill up both are verbs.

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

As verbs, fill up is a hyponym of eat; that is, fill up is a word with a more specific, narrower meaning than eat:

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