mortal sin vs avaritia

mortal sin and avaritia both are nouns.

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

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

mortal sin: an unpardonable sin entailing a total loss of grace
avaritia: reprehensible acquisitiveness; insatiable desire for wealth (personified as one of the deadly sins)

mortal sin (noun)	avaritia (noun)
an unpardonable sin entailing a total loss of grace	reprehensible acquisitiveness; insatiable desire for wealth (personified as one of the deadly sins)