Possibly derived from Proto-Indo-European *h₂ep- (“water”), compare Proto-Celtic *abū (“river”), if the word originally referred to a "water sprite". Compare Proto-Celtic *abankos (“water creature”), from whence Welsh afanc and Breton avank (“beaver”), Middle Irish abacc (“dwarf”).
It is however more popular to assume an ancient loanword instead, ultimately probably from an unidentified non-Indo-European language of regions in Africa or Asia where monkeys are native. The same wanderwort may be reflected in Hebrew קוֹף (qōf), Akkadian uqūpu, Egyptian gfj, Middle Persian [script needed] (kpyk' /kabīg/), Sanskrit कपि (kapi), all meaning “monkey, ape”, and Ancient Greek κῆπος (kêpos, “long-tailed monkey”). As Kroonen notes, the lack of an initial velar consonant in Germanic implies that the foreign word entered at a very early pre-Germanic stage, such that it was borrowed with an initial laryngeal.
|masculine an-stemDeclension of *apô (masculine an-stem)|
- Proto-West Germanic: *apō
- Old English: apa
- Old Frisian: *apa
- Old Saxon: apo
- Old Dutch: *apo
- Old High German: affo
- → Proto-Slavic: *opъ
- ⇒ Proto-Slavic: *opica (see there for further descendants)
- Old Norse: api m