boot - protective casing for something that resembles a leg

gear case, gearbox - the shell (metal casing) in which a train of gears is sealed

grandfather clock, longcase clock - a pendulum clock enclosed in a tall narrow case

housing - a protective cover designed to contain or support a mechanical component

jacket - the tough metal shell casing for certain kinds of ammunition

covering - an artifact that covers something else (usually to protect or shelter or conceal it)

pneumatic tire, pneumatic tyre - a tire made of reinforced rubber and filled with compressed air; used on motor vehicles and bicycles etc

doorway, room access, door, threshold - the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close; "he stuck his head in the doorway"

frame, framing, framework - a structure supporting or containing something

window - a framework of wood or metal that contains a glass windowpane and is built into a wall or roof to admit light or air