The Collaborative International Dictionary of English v.0.48:

Spider web \Spi"der web"\, or Spider's web \Spi"der's web"\ .
   (Zool.)
   The silken web which is formed by most kinds of spiders,
   particularly the web spun to entrap their prey; -- also
   called cobweb. See Geometric spider, Triangle spider,
   under Geometric, and Triangle.
   [1913 Webster]