The Collaborative International Dictionary of English v.0.48:

Hackberry \Hack"ber`ry\ (h[a^]k"b[e^]r`r[y^]), n. (Bot.)
   A genus of trees (Celtis) related to the elm, but bearing
   drupes with scanty, but often edible, pulp. Celtis
   occidentalis is common in the Eastern United States. --Gray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

U.S. Gazetteer Places (2000):

Hackberry, LA -- U.S. Census Designated Place in Louisiana
   Population (2000):    1699
   Housing Units (2000): 818
   Land area (2000):     82.241483 sq. miles (213.004455 sq. km)
   Water area (2000):    11.443713 sq. miles (29.639080 sq. km)
   Total area (2000):    93.685196 sq. miles (242.643535 sq. km)
   FIPS code:            32405
   Located within:       Louisiana (LA), FIPS 22
   Location:             29.986485 N, 93.397190 W
   ZIP Codes (1990):     70645
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Hackberry, LA
    Hackberry


U.S. Gazetteer Places (2000):

Hackberry, TX -- U.S. town in Texas
   Population (2000):    544
   Housing Units (2000): 162
   Land area (2000):     0.537053 sq. miles (1.390962 sq. km)
   Water area (2000):    0.001543 sq. miles (0.003996 sq. km)
   Total area (2000):    0.538596 sq. miles (1.394958 sq. km)
   FIPS code:            31715
   Located within:       Texas (TX), FIPS 48
   Location:             33.150134 N, 96.918702 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Hackberry, TX
    Hackberry