thin out vs trim back

thin out and trim back both are verbs.

Word	Noun	Adjective	Verb	Adverb
thin out	No	No	Yes	No
trim back	No	No	Yes	No

As verbs, trim back is a hypernym of thin out; that is, trim back is a word with a broader meaning than thin out:

Other hypernyms of thin out include bring down, cut, cut back, cut down, reduce, trim, trim down.

thin out (verb)	trim back (verb)
make sparse	cut down on; make a reduction in
become sparser
lessen the strength or flavor of a solution or mixture