A cantilever is a girder or beam that supports a bridge or another large structure. Cantilevers are attached only at one end, like a rigid diving board.
Structures that stick out sideways from a vertical support are cantilevers (hold your arm straight out from your body and it becomes a kind of cantilever). Engineers construct bridges using cantilevers, balancing them with counterweights or reinforcing them with girders and trusses. Cantilever bridges were originally called cantlapper bridges—from cant, or "slope," eventually combined with lever, from the Latin levare, "to raise."