From Middle Low German knobbe 'knot, lump,' part of a large family of Germanic kn- words meaning 'bump.'
A rounded handle on a door or drawer; a rounded lump or protuberance.
From Middle English knobbe, probably from Middle Low German knobbe or a related Germanic source. Related to knop 'button, knot' and knob's cousins knob, knop, knub all cluster around the idea of a rounded bump. The door-handle sense developed by the 17th century. Key roots: *gneu- (Proto-Indo-European: "lump, knot (uncertain)").