The first of these usages, widespread in British English, developed in the early 1900s, although a cornet of paper for carrying food or groceries was known in Shakespeare's time. The second usage, the musical instrument, which was originally a type of horn and later a kind of trumpet, dates from the 1400s. The instrumental sense turns up several times in Shakespeare as a stage direction, when a "flourish of cornets" is heard - meaning a fanfare (as at the beginning of All's Well That Ends Well, I.ii). In the main text of the plays, however, it is found just once, in a rather different sense. When Richard tells Lucy of "Somerset, who in proud heartDoth stop my cornets" (Henry VI Part 1, IV.iii.25 ), the sense is of a "troop of cavalry". He means that Somerset is withholding his cavalrymen.
David Crystal is author, with Ben Crystal, of Shakespeare's Words, published by Penguin