burden vs imposition

burden and imposition both are nouns.

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

As nouns, imposition is a hyponym of burden; that is, imposition is a word with a more specific, narrower meaning than burden:

Other hyponyms of burden include dead weight, fardel, pill.

burden (noun)	imposition (noun)
weight to be borne or conveyed	the act of imposing something (as a tax or an embargo)
the central idea that is expanded in a document or discourse	an uncalled-for burden
an onerous or difficult concern
the central meaning or theme of a speech or literary work

burden (verb)	imposition (verb)
impose a task upon, assign a responsibility to
weight down with a load