Page "False etymology" Paragraph 3

Some etymologies are part of urban legends, and seem to respond to a general taste for the surprising, counterintuitive and even scandalous.

One common example has to do with the phrase rule of thumb, meaning a rough measurement.

An urban legend has it that the phrase refers to an old English law under which a man could legally beat his wife with a stick no thicker than his thumb ( though no such law ever existed ).