endometrium vs endometrial

endometrium is a noun but endometrial is not a noun.

Word	Noun	Adjective	Verb	Adverb
endometrium	Yes	No	No	No
endometrial	No	Yes	No	No

endometrium (noun)	endometrial (noun)
(pregnancy) the mucous membrane that lines the uterus; thickens under hormonal control and (if pregnancy does not occur) is shed in menstruation; if pregnancy occurs it is shed along with the placenta at parturition

endometrium (adjective)	endometrial (adjective)
	of or relating to the endometrium