undo vs loosen

undo and loosen both are verbs.

Word	Noun	Adjective	Verb	Adverb
undo	No	No	Yes	No
loosen	No	No	Yes	No

As verbs, undo and loosen are synonyms defined as:

Other synonyms of undo include untie.

undo (verb)	loosen (verb)
cancel, annul, or reverse an action or its effect	become loose or looser or less tight
cause to become loose	make loose or looser
remove the outer cover or wrapping of	make less dense
deprive of certain characteristics	disentangle and raise the fibers of
cause the ruin or downfall of	cause to become loose
	become less severe or strict
	make less severe or strict