realty vs mortmain

realty and mortmain both are nouns.

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

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

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

Other hyponyms of realty include acres, demesne, estate, land, landed estate, land, dead hand.

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