What is the meaning of word portcullis?

A portcullis is a heavy, vertically sliding gate typically made of wood or metal and hung from chains so that it can be raised or lowered in front of a doorway or a passage between rooms or buildings. Portcullises were commonly used in medieval castles and fortified cities to control entry and exit points and provide an additional layer of defense against attackers. They were designed to be difficult to break down and often had spikes or other obstructions on the lower edge to deter any attempts to pry them open or scale them.