diestrual vs diestrum

diestrual is not a noun while diestrum is a noun.

Word	Noun	Adjective	Verb	Adverb
diestrual	No	Yes	No	No
diestrum	Yes	No	No	No

diestrual (noun)	diestrum (noun)
	(of animals having several estrous cycles in one breeding season) a state or interval of sexual inactivity or quiescence between periods of activity

diestrual (adjective)	diestrum (adjective)
(of animals that have several estrous cycles in one breeding season) in a period of sexual inactivity