Source : Webster's Revised Unabridged Dictionary (1913)

Hackberry \Hack"ber`ry\, n. (Bot.)
   A genus of trees ({Celtis}) related to the elm, but bearing
   drupes with scanty, but often edible, pulp. {C. occidentalis}
   is common in the Eastern United States. --Gray.

Source : WordNet®

hackberry
     n 1: any of various trees of the genus Celtis having
          inconspicuous flowers and small berrylike fruits [syn: {nettle
          tree}]
     2: small edible dark purple to black berry with large pits;
        southern United States [syn: {sugarberry}]