What does "bowstring" mean?

Bowstring: A string used by the Turks for strangling offenders. Bowstring bridge, a bridge formed of an arch of timber or iron, often braced, the thrust of which is resisted by a tie forming a chord of the arch. -- Bowstring girder, an arched beam strengthened by a tie connecting its two ends. -- Bowstring hemp (Bot.), the tenacious fiber of the Sanseviera Zeylanica, growing in India and Africa, from which bowstrings are made. Balfour.