mortal sin vs invidia

mortal sin and invidia both are nouns.

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

As nouns, invidia is a hyponym of mortal sin; that is, invidia is a word with a more specific, narrower meaning than mortal sin:

mortal sin: an unpardonable sin entailing a total loss of grace
invidia: spite and resentment at seeing the success of another (personified as one of the deadly sins)

mortal sin (noun)	invidia (noun)
an unpardonable sin entailing a total loss of grace	spite and resentment at seeing the success of another (personified as one of the deadly sins)