NOUN (3)

1. any of various dark-fruited as distinguished from blue-fruited blueberries;

2. any of several shrubs of the genus Gaylussacia bearing small berries resembling blueberries;

3. blue-black berry similar to blueberries and bilberries of the eastern United States;

The Collaborative International Dictionary of English v.0.48:

Huckleberry \Huc"kle*ber`ry\, n. [Cf. Whortleberry.] (Bot.)
   (a) The edible black or dark blue fruit of several species of
       the American genus Gaylussacia, shrubs nearly related
       to the blueberries (Vaccinium), and formerly confused
       with them. The commonest huckelberry comes from
       Gaylussacia resinosa.
   (b) The shrub that bears the berries. Called also
       whortleberry.
       [1913 Webster]

   Squaw huckleberry. See Deeberry.
      [1913 Webster]

WordNet (r) 3.0 (2006):

huckleberry
    n 1: any of various dark-fruited as distinguished from blue-
         fruited blueberries
    2: any of several shrubs of the genus Gaylussacia bearing small
       berries resembling blueberries
    3: blue-black berry similar to blueberries and bilberries of the
       eastern United States