The Collaborative International Dictionary of English v.0.48:

Blue bonnet \Blue" bon`net\ or Blue-bonnet \Blue"-bon`net\, n.
   1. A broad, flat Scottish cap of blue woolen, or one wearing
      such cap; a Scotchman.
      [1913 Webster]

   2. (Bot.) A plant. Same as Bluebottle.
      [1913 Webster]

   3. (Zool.) The European blue titmouse (Parus c[oe]ruleus);
      the bluecap.
      [1913 Webster]