Dutch for blockhead, I believe. There was a wonderful children's book about Anton von Leeuwenhoek, the final lines of which were:
"This man is mad!" the people said. "This Anton's crazy in the head! He says he's seen a horsefly's brain. We ought to ship him off to Spain." (overleaf of Mr. Leeuwenhoek, looking sad, in a boat by a sign pointing forward, labelled 'To Spain.') They called him domkop, which means 'dope'. And that's how we got the microscope.