Wights can be deadly if you lack high magic cancellation, and are one of the many monsters that exemplify the increased need for a drain resistance source much earlier in SLASH'EM. Luckily, there are plentiful cloak sources of MC3, which will render their drain attacks all but harmless.
Unlike the corpses of actual wraiths, wight corpses are useless to players: they are generated too old for sacrifice, will likely inflict food poisoning and do not grant any nutrition, experience levels or intrinsics, though a Necromancer's pet ghoul will happily dig into them.
The wight is one of many new monsters introduced in SLASH 6, an ancestor variant of SLASH'EM.
A wight (Old English wiht) is a mythical sentient being, often undead. The Old English word originally described a living human being, and has since come to be used within fantasy works such as A Song of Ice and Fire and Vampire: The Masquerade to describe immortal ghost-like beings. The earliest example of the modern wight is in William Morris's 1869 translation of the Grettis saga, a work of Icelandic family prose; here, haugbui (referring to undead monsters Glámr and Kárr) is translated as "barrow-wight".
NetHack most likely derives wights from their 1974 inclusion in Dungeons & Dragons, where they are light-hating evil spirits that can only be damaged by silver and magical weapons. Wights can drain life energy levels with their single attack, reducing the target's experience level by one; humans fully drained by wights become half-strength wights themselves under their killer's control. Wight are immune to charming, holding/paralyzing spells, poison, and sleep- or cold-based spells - holy water can damage a wight, and the "raise dead" spell can outright destroy them.
When he came to himself again, for a moment he could recall nothing except a sense of dread. Then suddenly he knew that he was imprisoned, caught hopelessly; he was in a barrow. A Barrow-wight had taken him, and he was probably already under the dreadful spells of the Barrow-wights about which whispered tales spoke. He dared not move, but lay as he found himself: flat on his back upon a cold stone with his hands on his breast.