flood vs fill up

flood is a noun but fill up is not a noun.

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

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

Other hypernyms of flood include fill.

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

Other hypernyms of flood include fill, make full.

flood (noun)	fill up (noun)
the act of flooding; filling to overflowing
a large flow
light that is a source of artificial illumination having a broad beam; used in photography
the occurrence of incoming water (between a low tide and the following high tide)
the rising of a body of water and its overflowing onto normally dry land
an overwhelming number or amount

flood (verb)	fill up (verb)
cover with liquid, usually water	make full, also in a metaphorical sense
become filled to overflowing	become full
fill quickly beyond capacity; as with a liquid	eat until one is sated
supply with an excess of	fill or stop up