tighten up vs tighten

tighten up and tighten both are verbs.

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

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

Other synonyms of tighten up include constrain, stiffen.

tighten up (verb)	tighten (verb)
severely restrict in scope or extent	become tight or tighter
	make tight or tighter
	severely restrict in scope or extent
	narrow or limit