The Collaborative International Dictionary of English v.0.48:

Dewberry \Dew"ber`ry\, n. (Bot.)
   (a) The fruit of certain species of bramble (Rubus); in
       England, the fruit of Rubus c[ae]sius, which has a
       glaucous bloom; in America, that of Rubus canadensis
       and Rubus hispidus, species of low blackberries.
   (b) The plant which bears the fruit.
       [1913 Webster]

             Feed him with apricots and dewberries. --Shak.
       [1913 Webster]

WordNet (r) 3.0 (2006):

dewberry
    n 1: any of several trailing blackberry brambles especially of
         North America [syn: dewberry, dewberry bush, running
         blackberry]
    2: blackberry-like fruits of any of several trailing blackberry
       bushes