/summa/SS/SSII/SS_Q72:
We must now consider injuries inflicted by words uttered extrajudicially. We shall consider (1) reviling, (2) backbiting, (3) tale bearing, (4) derision, (5) cursing.
Under the first head there are four points of inquiry:
(1) What is reviling?
(2) Whether every reviling is a mortal sin?
(3) Whether one ought to check revilers?
(4) Of the origin of reviling.