spit vs rain down

spit is a noun but rain down is not a noun.

Word	Noun	Adjective	Verb	Adverb
spit	Yes	No	Yes	No
rain down	No	No	Yes	No

As verbs, rain down is a hypernym of spit; that is, rain down is a word with a broader meaning than spit:

Other hypernyms of spit include rain.

spit (noun)	rain down (noun)
the act of spitting (forcefully expelling saliva)
a skewer for holding meat over a fire
a clear liquid secreted into the mouth by the salivary glands and mucous glands of the mouth; moistens the mouth and starts the digestion of starches
a narrow strip of land that juts out into the sea

spit (verb)	rain down (verb)
expel or eject (saliva or phlegm or sputum) from the mouth	precipitate as rain
utter with anger or contempt
drive a skewer through
rain gently