Check out the Sins against faith again. I think cowardice would fit in there.
Agree it would arguably fit in a broad category as would many of the sins identified, but the catalogue should be at least as specific as Scripture and include the chart toppers. Actually, cannot recall ever hearing a sermon or homily on the sin of cowardice, specifically. But it's at the top of, and specifically called out in, St. John's list. Peace, A