The Collaborative International Dictionary of English v.0.48:

Bowstring \Bow"string`\, n.
   1. The string of a bow.
      [1913 Webster]

   2. A string used by the Turks for strangling offenders.
      [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bowstring \Bow"string`\, v. t. [imp. & p. p. Bowstringedor
   Bowstrung; p. pr. & vb. n. Bowstringing.]
   To strangle with a bowstring.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bowstring
    n 1: the string of an archer's bow