The wight was originally an Old English word (wiht) meaning "creature, being," but came to denote a corpse inhabited by a barrow-haunting malign spirit, and by way of the Norse draugr and Tolkien’s barrow-wights it settled into tabletop role-playing as an undead. It drains a victim’s life force to kill, then raises the slain as another wight, swelling its numbers.
In multiplying its kind by draining life, it belongs with the zombie and vampire among the contagious undead.