unburden vs burden

unburden is not a noun while burden is a noun.

Word	Noun	Adjective	Verb	Adverb
unburden	No	No	Yes	No
burden	Yes	No	Yes	No

unburden (noun)	burden (noun)
	weight to be borne or conveyed
	the central idea that is expanded in a document or discourse
	an onerous or difficult concern
	the central meaning or theme of a speech or literary work

unburden (verb)	burden (verb)
take the burden off; remove the burden from	impose a task upon, assign a responsibility to
free or relieve (someone) of a burden	weight down with a load