oyster [OE] This goes back ultimately to Greek ostreon, which was related to ostrakon ‘shell or tile’ and is linked to *ostracize. The possibility that on opening an oyster you might find a pearl has given us an expression that goes back to Shakespeare. In The Merry Wives of Windsor the boastful Pistol brags to Falstaff, ‘Why then, the world’s mine oyster, which I with sword will open.’