[1] : The Collaborative International Dictionary of English v.0.48

arachnida \arach"nida\, n. pl. nl., fr. gr. ? spider.
   zool.
   one of the classes of arthropoda. see illustration in
   appendix.
   1913 webster

   note: they have four pairs of legs, no antennae nor wings,
         a pair of mandibles, and one pair of maxillae or
         palpi. the head is usually consolidated with the
         thorax. the respiration is either by trancheae or by
         pulmonary sacs, or by both. the class includes three
         principal orders: araneina, or spiders;
         arthrogastra, including scorpions, etc.; and
         acarina, or mites and ticks.
         1913 webster
see also:
araneina arthrogastra acarina 

[2] : WordNet (r) 2.0

arachnida
     n : a large class of arthropods including spiders and ticks and
         scorpions and daddy longlegs; have four pairs of walking
         legs and no wings syn: class arachnida
see also:
class arachnida 

Arachnida >> A Words
Arachnida, definition of term: Arachnida
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