The Collaborative International Dictionary of English v.0.48:

Arthropoda \Ar*throp"o*da\, n. pl. [NL., fr. Gr. 'a`rqron joint
   + -poda.] (Zool.)
   A large division of Articulata, embracing all those that have
   jointed legs. It includes Insects, Arachnida, Pychnogonida,
   and Crustacea. -- Ar*throp"o*dal, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Arthropoda
    n 1: jointed-foot invertebrates: arachnids; crustaceans;
         insects; millipedes; centipedes [syn: Arthropoda, phylum
         Arthropoda]