This word came to be increasingly used in its present-day meanings during the 16th century, as people increasingly travelled abroad. But Shakespeare uses the word differently. When Cerimon opens a chest washed up on shore and discovers Thaisa's body, he exclaims "A passport too!" (Pericles, III.ii.64). As Thaisa was thought to be dead when Pericles had the chest thrown from his ship, it can hardly be the modern sense. Rather it refers to a document giving an account of who she is. And when Helena shows Bertram's letter of rejection to the Countess saying "here's my passport" (All's Well That Ends Well, III.ii.55) - meaning that she will use it as a reason for following him - it has a more specialised sense. She is comparing the letter to the licence given to an inmate of an institution to travel as a beggar, and her choice of the word speaks volumes.
David Crystal is author, with Ben Crystal, of Shakespeare's Words, published by Penguin