Origins
The word 'hell' is, at its etymological core, not about fire and punishment but about concealment — the hidden realm, the covered place, the world beneath the surface where the dead are hidden from the living. It descends from Old English 'hell' (the underworld, the abode of the dead), from Proto-Germanic *haljō (the concealed place, the underworld), from PIE *ḱel- (to cover, to conceal, to hide).
The Proto-Germanic form *haljō is reflected across the Germanic languages: Old Norse 'hel' (the underworld, and the name of its ruling goddess), Old High German 'hella' (modern German 'Hölle'), Old Saxon 'hellia,' Old Frisian 'helle,' Dutch 'hel,' Gothic 'halja,' and Swedish 'helvete' (from 'hel' + 'víti,' punishment). In all these languages, the original meaning was simply 'the realm of the dead' — a neutral, morally unmarked underworld, not a place of punishment.
In pre-Christian Germanic cosmology, Hel was both a place and a person. The Norse goddess Hel, daughter of Loki, ruled the underworld realm also called Hel, where those who died of sickness, old age, or other unremarkable causes went after death (warriors slain in battle went to Valhalla instead). The realm of Hel was not a place of torment — it was cold, dim, and quiet, but not punitive. The dead simply continued a diminished existence in the hidden world below.
Latin Roots
The association of hell with fire, torment, and moral punishment came from Christianity, which mapped the concept of Gehenna (Greek 'Géenna,' from Hebrew 'Gê Hinnōm,' the Valley of Hinnom outside Jerusalem, associated with fire and child sacrifice) onto the existing Germanic word for the underworld. Christian missionaries translating Latin 'infernus' (the lower realm) chose the familiar Germanic word 'hell' but filled it with entirely new content: eternal fire, divine judgment, punishment for sin. The result is a pre-Christian word carrying Christian theology — a linguistic palimpsest.
The PIE root *ḱel- (to cover, to hide) is remarkably productive in English. 'Helmet' comes from Proto-Germanic *helmaz (a covering for the head), from the same root. 'Conceal' comes from Latin 'con-' + 'cēlāre' (to hide completely). 'Cell' comes from Latin 'cella' (a small room, a covered space — originally a storeroom, later a monk's chamber, then a prison chamber, and finally a biological unit). 'Cellar' is from the same Latin 'cella.' 'Occult' comes from Latin 'occultus' (hidden, secret), from 'ob-' (over) + the root of 'cēlāre.' 'Color' may also derive from this root, through Latin 'color' (concealing cover, hue — that which covers a surface), though this etymology is debated.
The word 'apocalypse,' by an elegant contrast, means the exact opposite of 'hell' etymologically: from Greek 'apokálypsis' (ἀποκάλυψις, uncovering, revelation), from 'apo-' (away from) + 'kalýptein' (to cover). The apocalypse is 'the uncovering' — the moment when what was hidden is revealed. Hell hides; apocalypse reveals.