freshen up vs freshen

freshen up and freshen both are verbs.

Word	Noun	Adjective	Verb	Adverb
freshen up	No	No	Yes	No
freshen	No	No	Yes	No

As verbs, freshen up and freshen are synonyms defined as:

Other synonyms of freshen up include refresh, refreshen.

freshen up (verb)	freshen (verb)
become or make oneself fresh again	make fresh again
make brighter and prettier	become or make oneself fresh again
	make (to feel) fresh