inundation vs the Flood

inundation and the Flood both are nouns.

Word	Noun	Adjective	Verb	Adverb
inundation	Yes	No	No	No
the Flood	Yes	No	No	No

As nouns, the Flood is a hyponym of inundation; that is, the Flood is a word with a more specific, narrower meaning than inundation:

inundation: the rising of a body of water and its overflowing onto normally dry land
the Flood: (Biblical) the great deluge that is said in the Book of Genesis to have occurred in the time of Noah; it was brought by God upon the earth because of the wickedness of human beings

Other hyponyms of inundation include debacle, flash flood, flashflood, Noachian deluge, Noah's flood, Noah and the Flood.

inundation (noun)	the Flood (noun)
the rising of a body of water and its overflowing onto normally dry land	(Biblical) the great deluge that is said in the Book of Genesis to have occurred in the time of Noah; it was brought by God upon the earth because of the wickedness of human beings
an overwhelming number or amount