Source : Webster's Revised Unabridged Dictionary (1913)

Prawn \Prawn\, n. [OE. prane, of unknown origin; cf. L. perna a
   sea mussel.] (Zo["o]l.)
   Any one of numerous species of large shrimplike Crustacea
   having slender legs and long antenn[ae]. They mostly belong
   to the genera {Pandalus}, {Pal[ae]mon}, {Pal[ae]monetes}, and
   {Peneus}, and are much used as food. The common English prawn
   is {Pal[ae]mon serratus}.

   Note: The name is often applied to any large shrimp.