undead

Etymology

From Middle English undede, equivalent to un- + dead. The first attestation is from around 1400. Usage as a noun is attested from the early 20th century onwards.

adj

1. Pertaining to a corpse, though having qualities of life.
2. (horror fiction) Being animate, though non-living.
   When Anna and John finally break out of their self-centered bubbles to the shock that they must battle to the death an undead neighbor in a giant snowman costume, it plays like a poignant comment on movie teenagers' tendency to indulge their inner lives, ignorant of the world around them. 27 November 2018, April Wolfe, “Anna And The Apocalypse is a Holiday-horror Cocktail of Singing, Maiming, and Clichés”, in The A.V. Club, archived from the original on 2019-11-04

noun

1. (horror fiction) Those creatures which are undead; that is, dead yet still animate.
   In the zombie movie, an army of the undead accosted some nubile skinny-dipping teenagers.
   Were another of the Un-Dead, like him, to try to do what he has done, perhaps not all the centuries of the world that have been, or that will be, could aid him. 1897, Bram Stoker, Dracula, New York: Doubleday & McClure, published 1899, page xxiv. 319
   Harley got devoured by the undead / Lurking down in some old wizard's tomb / You can say there's no such thing as zombies / But that's how Harley Warren met his doom 2006, The H. P. Lovecraft Historical Society, “Harley Got Devoured by the Undead”, in An Even Scarier Solstice
   It’s an episode of characters returning to their own pasts as different people. They can retrench like Cersei, back on her bullshit, I mean, warpath. Or they can adapt, like The Hound. Neither way necessarily ensures success, but we know the archmaester isn’t unequivocally right. We’ve seen dragons reborn and armies of the undead. I wouldn’t be so sure that Wall will stand forever. July 16, 2017, Brandon Nowalk, “Chickens and dragons come home to roost on Game Of Thrones (newbies)”, in The Onion AV Club

noun

1. (horror fiction) A creature that is undead; that is, dead but still animate.
   "You will do me a service," the undead said to him. 1983, Tanith Lee, The Wars of Vis
   Innocent VIII lent credibility to the actual existence of undeads, an action that perpetuated, and even stimulated, vampire hysteria. 1997, Carol Margaret Davison, Paul Simpson-Housley, Bram Stoker's Dracula: sucking through the century, 1897-1997