An old implement which was used for hand-washing clothes. It consisted of a copper dome full of holes attached to a long wooden handle.
A dolly could also be used for the same purpose, but this implement had several legs radiating from a wooden disc (looking rather like a small stool), and the long handle had a handle-bar arrangement at the top for maximum leverage.
A person exhibiting foolish or flighty behavior might be likened to a posser-head.
Before twin-tubs you had to use a posser and a mangle.