downfall vs rain

downfall and rain both are nouns.

Word	Noun	Adjective	Verb	Adverb
downfall	Yes	No	No	No
rain	Yes	No	Yes	No

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

downfall: the falling to earth of any form of water (rain or snow or hail or sleet or mist)
rain: water falling in drops from vapor condensed in the atmosphere

Other hyponyms of downfall include fine spray, hail, rainfall, sleet, snow, snowfall, virga.

downfall (noun)	rain (noun)
a sudden decline in strength or number or importance	anything happening rapidly or in quick successive
failure that results in a loss of position or reputation	water falling in drops from vapor condensed in the atmosphere
the falling to earth of any form of water (rain or snow or hail or sleet or mist)	drops of fresh water that fall as precipitation from clouds

downfall (verb)	rain (verb)
	precipitate as rain