The Collaborative International Dictionary of English v.0.48:

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. See Spin.]
   1. (Zool.) 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.
      [1913 Webster]

   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
         Saltigradae), the wolf spiders, or Citigradae (see
         under Wolf), the crab spiders, or Laterigradae (see
         under Crab), the garden, or geometric, spiders, or
         Orbitellae (see under Geometrical, and Garden),
         and others. See Bird spider, under Bird, Grass
         spider, under Grass, House spider, under House,
         Silk spider, under Silk.
         [1913 Webster]

   2. (Zool.) Any one of various other arachnids resembling the
      true spiders, especially certain mites, as the red spider
      (see under Red).
      [1913 Webster]

   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.
      [1913 Webster]

   4. A trevet to support pans or pots over a fire.
      [1913 Webster]

   5. (Mach.) A skeleton, or frame, having radiating arms or
      members, often connected by crosspieces; as, a casting
      forming the hub and spokes to which the rim of a fly wheel
      or large gear is bolted; the body of a piston head; a
      frame for strengthening a core or mold for a casting, etc.
      [1913 Webster]

   Spider ant. (Zool.) Same as Solitary ant, under
      Solitary.

   Spider crab (Zool.), any one of numerous species of maioid
      crabs having a more or less triangular body and ten long
      legs. Some of the species grow to great size, as the great
      Japanese spider crab (Macrocheira Kempferi), measuring
      sometimes more than fifteen feet across the legs when they
      are extended.

   Spider fly (Zool.), any one of numerous species of
      parasitic dipterous insects of the family Hippoboscidae.
      They are mostly destitute of wings, and live among the
      feathers of birds and the hair of bats. Called also bird
      tick, and bat tick.

   Spider hunter (Zool.), any one of several species of East
      Indian sunbirds of the genus Arachnothera.

   Spider lines, filaments of a spider's web crossing the
      field of vision in optical instruments; -- used for
      determining the exact position of objects and making
      delicate measurements. Fine wires, silk fibers, or lines
      on glass similarly placed, are called spider lines.

   Spider mite. (Zool.)
      (a) Any one of several species of parasitic mites of the
          genus Argas and allied genera. See Argas.
      (b) Any one of numerous small mites injurious to plants.


   Spider monkey (Zool.), any one of numerous species of South
      American monkeys of the genus Ateles, having very long
      legs and a long prehensile tail.

   Spider orchis (Bot.), a European orchidaceous plant
      (Ophrys aranifera), having flowers which resemble
      spiders.

   Spider shell (Zool.), any shell of the genus Pteroceras.
      See Pteroceras.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spider
    n 1: predatory arachnid with eight legs, two poison fangs, two
         feelers, and usually two 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: spider, wanderer]
    3: a skillet made of cast iron

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "spider":
   Chilopoda, Chordata, Echiuroidea, Ectoprocta, Entoprocta,
   Monoplacophora, Nemertinea, Phoronidea, arachnid, arthropod,
   beetle, bug, caterpillar, centipede, chilopod, daddy longlegs,
   diplopod, fly, harvestman, hexapod, insect, jenny, larva, maggot,
   millepede, millipede, mite, mule, nymph, scorpion, silkworm,
   skillet, spinner, spinning frame, spinning jenny, spinster,
   tarantula, throstle, tick



The Jargon File (version 4.4.7, 29 Dec 2003):

spider


    The Web-walking part of a search engine that collects pages for indexing in
    the search engine's database. Also called a bot. The best-known spider is
    Scooter, the web-walker for the Alta Vista search engine.


The Free On-line Dictionary of Computing (30 December 2018):

spider

    (Or "robot", "crawler") A program that
   automatically explores the 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)


Easton's 1897 Bible Dictionary:

Spider
   The trust of the hypocrite is compared to the spider's web or
   house (Job 8:14). It is said of the wicked by Isaiah that they
   "weave the spider's web" (59:5), i.e., their works and designs
   are, like the spider's web, vain and useless. The Hebrew word
   here used is _'akkabish_, "a swift weaver."

     In Prov. 30:28 a different Hebrew word (semamith) is used. It
   is rendered in the Vulgate by stellio, and in the Revised
   Version by "lizard." It may, however, represent the spider, of
   which there are, it is said, about seven hundred species in
   Palestine.