thin out vs prune

thin out is not a noun while prune is a noun.

Word	Noun	Adjective	Verb	Adverb
thin out	No	No	Yes	No
prune	Yes	No	Yes	No

As verbs, prune is a hyponym of thin out; that is, prune is a word with a more specific, narrower meaning than thin out:

Other hyponyms of thin out include clip, crop, cut back, dress, lop, snip, trim.

thin out (noun)	prune (noun)
	dried plum

thin out (verb)	prune (verb)
make sparse	weed out unwanted or unnecessary things
become sparser	cultivate, tend, and cut back the growth of
lessen the strength or flavor of a solution or mixture