trim back vs shorten

trim back and shorten both are verbs.

Word	Noun	Adjective	Verb	Adverb
trim back	No	No	Yes	No
shorten	No	No	Yes	No

As verbs, shorten is a hyponym of trim back; that is, shorten is a word with a more specific, narrower meaning than trim back:

trim back: cut down on; make a reduction in
shorten: make shorter than originally intended; reduce or retrench in length or duration

trim back (verb)	shorten (verb)
cut down on; make a reduction in	become short or shorter
	make shorter than originally intended; reduce or retrench in length or duration
	reduce in scope while retaining essential elements
	edit by omitting or modifying parts considered indelicate
	make short or shorter