An Etymological Dictionary of the German Language/Alp
Alp, m., ‘nightmare, incubus,’ from MidHG. alp(b), m., ‘spectre, incubus, nightmare, oppression caused by nightmare’; prop. a term applied to mythical beings, AS. œlf, OIc. álfr, ‘elf, goblin’ (the Scandinavians distinguished between fairies of light and darkness); these appear to be identical with the OInd. ṛbhú, (lit. ‘ingenious, sculptor, artist’), the name of three clever genii (the king of the fairies was ṛbhukšán). By the ASaxons, nightmare was called œlfâdl, œlfsogoða, ‘elf-malady, elf-sickness (hiccough),’ (lumbago in the Eng. dialects is termed awfshots, AS. ylfa gesceot). Comp. further Elf (proper names like Alboin, Alfred, have Alb as their first component).