Translated by Olivier van Renswoude from his original Dutch piece.
Since the Middle Ages we have been using the word ape for a certain exotic four-handed animal. But this word was already in use in the Germanic world two thousand years ago and likely referred to an entirely different being, one from native folk belief: a deceptive and ghastly black horror which lurked in the water.
The Old Germanic form of this word was *apō. Hence come Old English apa (English ape), Old Saxon apo, Middle Dutch aep (Dutch aap), Old High German affo (German Affe) and Old Norse api (Swedish apa, Norwegian ape, Danish abe). Seeing as the animal was not found here originally, it is usually assumed that the word came from elsewhere as well, borrowed from a foreign language and related to words like Sanskrit kapí- and Hebrew qōf. Leading Norwegian etymologists Bjorvand and Lindeman, however, rejected such a connexion after a comprehensive treatment a few years ago and concluded that *apō is of unknown origin. Since it is not very likely that the Germanic people had a general word for a very rare exotic animal, the word probably meant something different originally.
If we then look at possible relations of *apō within Germanic, there is really only one to consider, namely *apōn ‘water, stream’, a feminine word that we find in many a Germanic river name, like *Wisapōn (now Weesp in the Netherlands), *Felapōn (now Velp in Flanders) en *Askapōn (now Aschaff in Germany). If this connexion is right, then the original *apō was a creature that had something to do with water.
This relation becomes more likely by a parallel in the Celtic languages, which are closely related to the Germanic languages. For Old Germanic *apōn ‘water, stream’ answers to Old Celtic *abon- ‘river’ (Old Irish ab, aub, Middle Welsh afon, Breton auon) and from this was formed –with diminutive suffix– the derivation *abankos (Old Irish abacc, Welsh afanc, Breton avank), the name of a certain water being. In Ireland abacc was used as a different name for the luchorpáin, dwarves who according to the stories lived in a world under water and sometimes tried to kidnap people to it. In the folklore of Wales the afanc is sometimes said to be black and very ugly, and according to a well known story it poses as a handsome man who wants to drag his victim into the water. Nowadays afanc is only used to refer to beavers.
Striking then is the likeness of an evil spirit from the Germanic world, whose name *nikwazaz is attested as Old English nicor (English nicker), Old Norse nykr (Swedish näck, Norwegian nøkk, nykk, Danish nøkke), Middle Dutch nicker, necker (Dutch nikker) and Middle Low German necker and a variant form *nikwasaz as Old High German nihhus, nichus (German Nix). According to folklore, this wight dwells in water, is black and ugly (in some descriptions very hairy) and seeks to catch folk. In the Scandinavian stories it can pose as a handsome man to lure folk into the water, but also as a white horse that leaps into the water when someone climbs on its back. Its name was also used for exotic aquatic animals: hippopotami in Old English and Old Norse and crocodiles in Old High German.
Based on the aforementioned, it is likely that *apō and *nikwazaz were synonyms, i.e. referred to one and the same evil water spirit. Then in the Middle Ages, when the Germanic world was introduced to dark, hairy, ugly exotic mammals who could mimic people, it made sense to identity these with –or mockingly name these after– the water spirits of folklore.
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