The most powerful attacks strike home with crushing force, and cause massive damage to their victim.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
Multiple Wounds (*)URL Copied!
Each wound inflicted by an attack with the Multiple Wounds special rule (after saves) is multiplied into more than one wound (remember that a model cannot suffer more wounds than it has on its profile). The exact number of wounds caused will vary from model to model and weapon to weapon, but will normally be shown in brackets as part of the special rule. For example, Multiple Wounds (2) would mean that each unsaved wound would multiply to 2 wounds, whilst Multiple Wounds (D6) would mean that each unsaved wound would multiply to D6 wounds. If a model is granted two sets of Multiple Wounds (like D3 and D6), use only the highest set before rolling.
Where the number of Multiple Wounds is generated by a dice roll, roll a dice separately for each unsaved wound and use the total of all the dice rolled for the final number of wounds inflicted.
Unless otherwise specified, Multiple Wounds only apply to close combat attacks.