Source : Webster's Revised Unabridged Dictionary (1913)

Brachyura \Brach`y*u"ra\, n. pl. [NL., fr. Gr. brachy`s short +
   ? tail.] (Zo["o]l.)
   A group of decapod Crustacea, including the common crabs,
   characterized by a small and short abdomen, which is bent up
   beneath the large cephalo-thorax. [Also spelt {Brachyoura}.]
   See {Crab}, and Illustration in Appendix.

Source : WordNet®

Brachyura
     n : an order of crustaceans (including true crabs) having a
         reduced abdomen folded against the ventral surface [syn:
         {suborder Brachyura}]