Well, it can’t become a common word here on this board, as tomndebb (see post #11 above) has declared its use to be a warnable offense here.
I haven’t seen a convincing reason to not just use “slander” for the concept of calumny.
From a practical standpoint, calumny covers both spoken and written communications so you can avoid the slander/libel distinction.
From the standpoint of eloquence, slander is a legal term and doesn’t carry the same connotation of judgment as calumny. Slander is illegal; calumny is *wrong *.
I knew neither of those words but I’ve heard of them. Oh, and I always thought it was “handsome cab”, now it makes sense!