mortmain vs immovable

mortmain and immovable both are nouns.

Word	Noun	Adjective	Verb	Adverb
mortmain	Yes	No	No	No
immovable	Yes	Yes	No	No

As nouns, immovable is a hypernym of mortmain; that is, immovable is a word with a broader meaning than mortmain:

mortmain: real property held inalienably (as by an ecclesiastical corporation)
immovable: property consisting of houses and land

Other hypernyms of mortmain include real estate, real property, realty.

mortmain (noun)	immovable (noun)
the oppressive influence of past events or decisions	property consisting of houses and land
real property held inalienably (as by an ecclesiastical corporation)

mortmain (adjective)	immovable (adjective)
	not able or intended to be moved