Source : Webster's Revised Unabridged Dictionary (1913)

Bilberry \Bil"ber*ry\, n.; pl. {Bilberries}. [Cf. Dan.
   b["o]lleb[ae]r bilberry, where b["o]lle is perh. akin to E.
   ball.]
   1. (Bot.) The European whortleberry ({Vaccinium myrtillus});
      also, its edible bluish black fruit.

            There pinch the maids as blue as bilberry. --Shak.

   2. (Bot.) Any similar plant or its fruit; esp., in America,
      the species {Vaccinium myrtilloides}, {V. c[ae]spitosum}
      and {V. uliginosum}.

Source : WordNet®

bilberry
     n 1: erect European blueberry having solitary flowers and
          blue-black berries [syn: {whortleberry}, {whinberry}, {blaeberry},
           {Viccinium myrtillus}]
     2: erect blueberry of western United States having solitary
        flowers and somewhat sour berries [syn: {thin-leaved
        bilberry}, {mountain blue berry}, {Viccinium membranaceum}]
     3: blue-black berries similar to American blueberries [syn: {whortleberry},
         {European blueberry}]