(architecture) An arch built in the body of a wall to relieve the pressure, as over a door or window.

A plug of soft metal in an opening in a steam boiler, designed to melt when the temperature rises to a certain point, and thus allow the escape of steam.

plural of safety arch

plural of safety plug

A mechanism for preventing accidents in machinery. / (underwater diving) A diver's pause at a certain depth when ascending, to prevent decompression sickness.

plural of safety stop

A fireproof curtain which can be lowered to stop the spread of fire between the auditorium and the stage

plural of safety curtain

Paper prepared as to resist alteration by chemical or mechanical means.

A rein for preventing a horse from running away.