1.NounA component of an aircraft wheel held in place by a metal alloy with a low melting point, such that, if the wheel is severely overheated (for instance, by heavy braking), pressure is released from the wheel and tire/tyre in a controlled manner rather than risking an explosion of the wheel assembly.
2.NounA collapsible dam or levee designed to give way in extreme flood conditions in order to divert water away from more important water-control structures.