The Collaborative International Dictionary of English v.0.48:

Tarantula \Ta*ran"tu*la\, n.; pl. E. Tarantulas, L.
   Tarantulae. [NL., fr. It. tarantola, fr. L. Tarentum, now
   Taranto, in the south of Italy.] (Zool.)
   Any one of several species of large spiders, popularly
   supposed to be very venomous, especially the European species
   (Tarantula apuliae). The tarantulas of Texas and adjacent
   countries are large species of Mygale. [Written also
   tarentula.]
   [1913 Webster]

   Tarantula killer, a very large wasp (Pompilus formosus),
      which captures the Texan tarantula (Mygale Hentzii) and
      places it in its nest as food for its young, after
      paralyzing it by a sting.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tarantula
    n 1: large southern European spider once thought to be the cause
         of tarantism (uncontrollable bodily movement) [syn:
         European wolf spider, tarantula, Lycosa tarentula]
    2: large hairy tropical spider with fangs that can inflict
       painful but not highly venomous bites

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "tarantula":
   arachnid, arthropod, beetle, bug, caterpillar, centipede, chilopod,
   daddy longlegs, diplopod, fly, harvestman, hexapod, insect, larva,
   maggot, millepede, millipede, mite, nymph, scorpion, spider,
   tick