rain vs shower

rain and shower both are nouns.

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

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

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

rain (noun)	shower (noun)
anything happening rapidly or in quick successive	washing yourself by standing upright under water sprayed from a nozzle
water falling in drops from vapor condensed in the atmosphere	a plumbing fixture that sprays water over you
drops of fresh water that fall as precipitation from clouds	a sudden downpour (as of tears or sparks etc) likened to a rain shower
	a party of friends assembled to present gifts (usually of a specified kind) to a person
	a brief period of precipitation
	someone who organizes an exhibit for others to see

rain (verb)	shower (verb)
precipitate as rain	take a shower; wash one's body in the shower
	provide abundantly with
	spray or sprinkle with
	expend profusely; also used with abstract nouns
	rain abundantly