mortal sin vs venial sin

mortal sin and venial sin both are nouns.

Word	Noun	Adjective	Verb	Adverb
mortal sin	Yes	No	No	No
venial sin	Yes	No	No	No

mortal sin (noun)	venial sin (noun)
an unpardonable sin entailing a total loss of grace	a pardonable sin regarded as entailing only a partial loss of grace