My cousin sister lost all her files to a malicious script on her pendrive, and I am fixing it right now (at the time of writing this). The unreliable pile of crap called OneDrive didn’t even back up properly, and well, Windows has gone so bad, it’s terrible,laggy and slow on a Ryzen 5800U with 8GB of RAM. I wish she was open to learning Linux desktop environments.
That’s the remnants of old British English, which probably preserved one if the features of Latin. It means “also/and”.
So penetration-cum-blast round means penetration-and-blast round. On second thought, this really doesn’t fix how wrong it sounds.