Chainsword
From Exterminatus Manual
++Weapons++
The Chainsword is the outcome of the Imperium combining a chainsaw and a sword creating a hybrid weapon. Typically one or mode edges of the blade have a set of moving blades running along it, these blades oscillate at high speed and produce a cutting action beyond the normal brute force of a simple blade.
This gives the weapon increased damage, as there is both the impact of the sword being swung and the effect of the blades along the edge biting into the target.