imposition vs encumbrance

imposition and encumbrance both are nouns.

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

As nouns, encumbrance is a hypernym of imposition; that is, encumbrance is a word with a broader meaning than imposition:

Other hypernyms of imposition include burden, incumbrance, load, onus.

imposition (noun)	encumbrance (noun)
the act of imposing something (as a tax or an embargo)	any obstruction that impedes or is burdensome
an uncalled-for burden	an onerous or difficult concern
	a charge against property (as a lien or mortgage)