op means upon, worn, up, upwards, exhausted, on
So I am now supposing that "sop" in English and Dutch share the same root, and that we've turned gravy into what we do to it. And "op," well, that sounds like "up" to me. But I wonder if Ruud had any other reading in mind!
Ruud Janssen, "Sop" (12 Aug 2005)
un violon d'ingres