action mechanism - the operating part that transmits power to a mechanism; "the piano had a very stiff action"gun - a weapon that discharges a missile at high velocity (especially from a metal tube or barrel) key - a lever that actuates a mechanism when depressed keyboard - device consisting of a set of keys on a piano or organ or typewriter or typesetting machine or computer or the like mechanism - device consisting of a piece of machinery; has moving parts that perform some function movement - the driving and regulating parts of a mechanism (as of a watch or clock); "it was an expensive watch with a diamond movement" piano action - action consisting of a system of levers that move a felt hammer to strike the strings when a key is depressed pump action, slide action - action mechanism in a modern rifle or shotgun; a back and forward motion of a sliding lever ejects the empty shell case and cocks the firearm and loads a new round |