Suppressive (X) "Weapons and other attacks that have the Suppressive (X) Special Rule have a chance of inflicting the Suppressed Status on the Target Unit."
If a Shooting Attack made for a Weapon or Model with this Special Rule inflicts one or more Hits on a Target Unit, that Target Unit must make a Cool Check in the Morale Sub-Phase of the same Player Turn. If this Check is failed then all Models in the Unit gain the Suppressed Status, and if the Check is passed then there is no further effect. The value of X attached to this Rule is applied as a negative modifier to the Cool Characteristic of Models in the Target Unit when making Checks caused by an attack with this Special Rule, if the attack includes multiple Weapons with different versions of this Special Rule the modifiers do not stack - use only the greatest modifier.