Like our words bus and mob, contracted by humorists of bygone years from the more pompous Latin terms omnibus and mobile vulgus respectively, the word “joke” came into our language in the seventeenth century as a contraction by some unknown wit of the Latin jocus, a jest.
The legend that John Milton originated the contraction cannot be proved, for the word does not appear in any of his writings.
He had the wit to have done so, however, as shown by his various facetious poems.