To make a knight by giving him a blow. Dr. Tusler says,
“The ancient method or knighting was by a box on the ear, implying that
it would be the last he would receive, as he would henceforth be free
to maintain his own honour.” The present ceremony is to tap the
shoulder with a sword. (Anglo-Saxon, dubban, to strike with a
blow.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
