Alexander Dyce, A General Glossary to Shakespeare's Works

murdering-piece HAMLET, iv. 5. 92. “A murdering-piece or murderer was a small piece of artillery; in Fr. meurtrière. It took its name from the loopholes and embrasures in towers and fortifications, which were so called. The portholes in the forecastle of a ship were also thus denominated. ‘Meurtriere, c'est un petit canonniere, comme celles des tours et murailles, ainsi appellé, parceque tirant par icelle a desceu, ceux ausquels on tire sont facilement meurtri.’ Nicot. ‘Visiere meurtriere, a port-hole for a murthering-piece in the forecastle of a ship.’ Cotgrave. Case-shot, filled with small bullets, nails, old iron, etc., was often used in these murderers. This accounts for the raking fire attributed to them in the text” (SINGER) . Cotgrave has also“Meurtrieres. Holes (in that part of a rampire that hangs ouer the gate) whereat the assailed let fall stones on the heads of theer too neere approaching aduersarie.”Murdering-pieces, if we may trust Coles, were not always“small;” for he gives “A Murdering-piece, Tormentum murale,” and afterwards “Tormentum murale, a great gun.” Lat. and Engl. Dict.