A way to give the same attack multiple times from a single attempt. If you hear this phrase before an attack, you need to defend against that Verbal twice in a row even though they only hit you once. From the Accelerant core rules:

"One single delivery causes multiple attacks to affect the target. "Double" causes two of the specified attack to be delivered. Each attack requires a separate defense."

"For example, a wizard calls out "Double 10 Damage by Fire" and throws a Packet that hits you. You must take two "10 Damage by Fire" attacks. "Resist Fire" would negate one of these attacks and you would still take one attack. You may use multiple defenses against these attacks."