From Middle Dutch eike, êke, from Old Dutch *eik, *ēk, from Proto-West Germanic *aik, from Proto-Germanic *aiks, from Proto-Indo-European *h₂eyǵ- (“oak”). The form in ei- is regular in south-eastern dialects, but may also have developed elsewhere after the adjective *eikīn (“oaken”, modern eiken), where umlaut would have hindered the monophthongisation.