Hellions are armed with a unique weapon called a hellglaive. It incorporates a splinter rifle and a set of vicious cutting blades that are capable of slicing a man in half as the Hellion swoops into close combat. The hellglaive can be used as a splinter rifle or a close combat weapon, but may not be used as both in the same turn. If the user charges into close combat then the hellglaive also adds +1 to their Strength for the first round of combat. The hellglaive requires two hands to use, so can't be combined with any other weapon. Characters taking a hellglaive must also take a Hellion skyboard.
Hellglaive
Source: Codex: Dark Eldar (1998), p. 14