From Middle Low German Kôpenhāgen, older Kôpenhāven, Kôpmanhāven, from Old Danish Køp(m)enhafn, Køpmannæhafn. The full form of the name translates to “merchants’ harbour” in both Low German and Danish. More contracted forms appear in both languages alongside, so there is no need to see the development as folk etymology (“buying harbour”, although it may have been interpreted thus by Low German…