posthaste

In the 16th century, the phrase "haste, post, haste" was used to inform posts (as couriers were then called) that a letter was urgent and must be hastily delivered. Posts would then speedily gallop along a route with a series of places at which to get a fresh horse or to relay the letter to a fresh messenger. William Shakespeare was one of the first to use a version of the phrase adverbially in Richard II. "Old John of Gaunt ... hath sent post haste / To entreat your Majesty to visit him," the Bard versified. He also used the phrase as an adjective (a use that is now obsolete) in Othello: "The Duke ... requires your haste-post-haste appearance," Lieutenant Cassio reports to the play's namesake. Today, the word still possesses a literary flair attributable to the Bard.