Source : Webster's Revised Unabridged Dictionary (1913)

Dobson \Dob"son\, n. (Zo["o]l.)
   The aquatic larva of a large neuropterous insect ({Corydalus
   cornutus}), used as bait in angling. See {Hellgamite}.

Source : WordNet®

dobson
     n 1: large brown aquatic larva of the dobsonfly; used as fishing
          bait [syn: {hellgrammiate}]
     2: large soft-bodied insect having long slender mandibles in
        the male; aquatic larvae often used as bait [syn: {dobsonfly},
         {dobson fly}, {Corydalus cornutus}]