It’s a dark wet evening in the west of Ireland and I’m cosying up with The Poolbeg Book of Irish Ghost Stories (1990), edited by the late author and literary editor David Marcus. His brief introduction contains a word too rare even to appear in the OED. But you’ll probably know or can guess what it means:
[Ghosts’] preferred outer abode was a dark wood; indoors they inhabited rambling old castles or, more latterly, unsaleable houses, stalking creaky corridors and draughty bedchambers to the accompaniment of howls, shrieks, moans, plods and clankings. It goes without saying that they were largely nocturnal creatures, preferring the small hours and often the most inclement of weather in which to conduct their business. Daylight, electric light, gaslight were eschewed. Candlelight, because they had the capacity to extinguish a candle and so create the maximum horripilatory effect, was welcomed.
Horripilatory is a technical word meaning hair-raising. The associated noun horripilation is much more common, though hardly an everyday term; it too refers to the physiological phenomenon often called gooseflesh or goosebumps, typically caused by cold or fear. It comes from Latin horripilāre “bristle with hairs”, formed from horrēre “bristle, tremble” + pilus “hair” (cf. the cosmetic terms epilation and depilation).
Horrēre lurks behind horror, horrendous, horrify, abhor and horrid (which originally meant bristling or shaggy); and it’s also seen in the obscure horrious “causing horror”, horrent “bristling or rough”, horrisonant and horrisonous “of horrible sound”, and abhorrible “detestable”. A pretty hair-raising bunch of words, wouldn’t you say?