Lewis Short
exōstra (noun F) = ἐξώστρα: .
* A machine in the theatre, by which the back part of the stage was turned towards the spectators; transf. of any thing public: quibuscum jam in exostra helluatur,Cic. Prov. Cons. 6, 14.
* A hanging bridge, applied by besiegers to the walls of a besieged city, Veg. Mil. 4, 21.
Charlton T. Lewis, Charles Short, A Latin Dictionary