Source : Webster's Revised Unabridged Dictionary (1913)

Spider \Spi"der\, n.[OE. spi[thorn]re, fr. AS. spinnan to spin;
   -- so named from spinning its web; cf. D. spin a spider, G.
   spinne, Sw. spindel. Seee {Spin}.]
   1. (Zo["o]l.) Any one of numerous species of arachnids
      comprising the order Araneina. Spiders have the mandibles
      converted into poison fangs, or falcers. The abdomen is
      large and not segmented, with two or three pairs of
      spinnerets near the end, by means of which they spin
      threads of silk to form cocoons, or nests, to protect
      their eggs and young. Many species spin also complex webs
      to entrap the insects upon which they prey. The eyes are
      usually eight in number (rarely six), and are situated on
      the back of the cephalothorax. See Illust. under
      {Araneina}.

   Note: Spiders are divided into two principal groups: the
         Dipneumona, having two lungs: and the Tetrapneumona,
         having four lungs. See {Mygale}. The former group
         includes several tribes; as, the jumping spiders (see
         {Saltigrad[ae]}), the wolf spiders, or {Citigrad[ae]}
         (see under {Wolf}), the crab spiders, or
         {Laterigrad[ae]} (see under {Crab}), the garden, or
         geometric, spiders, or {Orbitell[ae]} (see under
         {Geometrical}, and {Garden}), and others. See {Bird
         spider}, under {Bird}, {Grass spider}, under {Grass},
         {House spider}, under {House}, {Silk spider}, under
         {Silk}.

   2. (Zo["o]l.) Any one of various other arachnids resembling
      the true spiders, especially certain mites, as the red
      spider (see under {Red}).

   3. An iron pan with a long handle, used as a kitchen utensil
      in frying food. Originally, it had long legs, and was used
      over coals on the hearth.

   4. A trevet to support pans or pots over a fire.

Source : WordNet®

spider
     n 1: predatory arachnid that usually has silk-spinning organs at
          the back end of the body; they spin silk to make cocoons
          for eggs or traps for prey
     2: a computer program that prowls the internet looking for
        publicly accessible resources that can be added to a
        database; the database can then be searched with a search
        engine [syn: {wanderer}]
     3: a skillet made of cast iron

Source : Free On-Line Dictionary of Computing

spider
     
         (Or "robot", "crawler") A program that
        automatically explores the {World-Wide Web} by retrieving a
        document and recursively retrieving some or all the documents
        that are referenced in it.  This is in contrast with a normal
        {web browser} operated by a human that doesn't automatically
        follow links other than {inline images} and {URL redirection}.
     
        The {algorithm} used to pick which references to follow
        strongly depends on the program's purpose.  {Index}-building
        spiders usually retrieve a significant proportion of the
        references.  The other extreme is spiders that try to validate
        the references in a set of documents; these usually do not
        retrieve any of the links apart from redirections.
     
        The {standard for robot exclusion} is designed to avoid some
        problems with spiders.
     
        Early examples were {Lycos} and {WebCrawler}.
     
        {Home
        (http://info.webcrawler.com/mak/projects/robots/robots.html)}.
     
        (2001-04-30)