An Etymological Dictionary of the German Language/Annotated/Alp
Alp, masculine, ‘nightmare, incubus,’ from Middle High German alp(b), masculine, ‘spectre, incubus, nightmare, oppression caused by nightmare’; properly a term applied to mythical beings, Anglo-Saxon œlf, Old Icelandic álfr, ‘elf, goblin’ (the Scandinavians distinguished between fairies of light and darkness); these appear to be identical with the Old Indian ṛbhú, (literally ‘ingenious, sculptor, artist’), the name of three clever genii (the king of the fairies was ṛbhukšán). By the Anglo-Saxons, nightmare was called œlfâdl, œlfsogoða, ‘elf-malady, elf-sickness (hiccough),’ (lumbago in the English dialects is termed awfshots, Anglo-Saxon ylfa gesceot). Compare further Elf (proper names like Alboin, Alfred, have Alb as their first component).