deluge vs flashflood

deluge and flashflood both are nouns.

Word	Noun	Adjective	Verb	Adverb
deluge	Yes	No	Yes	No
flashflood	Yes	No	No	No

As nouns, flashflood is a hyponym of deluge; that is, flashflood is a word with a more specific, narrower meaning than deluge:

deluge: the rising of a body of water and its overflowing onto normally dry land
flashflood: a sudden local flood of great volume and short duration

deluge (noun)	flashflood (noun)
a heavy rain	a sudden local flood of great volume and short duration
the rising of a body of water and its overflowing onto normally dry land
an overwhelming number or amount

deluge (verb)	flashflood (verb)
fill or cover completely, usually with water
charge someone with too many tasks
fill quickly beyond capacity; as with a liquid