The Collaborative International Dictionary of English v.0.48:

Underwood \Un"der*wood`\, n.
   Small trees and bushes that grow among large trees; coppice;
   underbrush; -- formerly used in the plural.
   [1913 Webster]

         Shrubs and underwoods look well enough while they grow
         within the shade of oaks and cedars.     --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

underwood
    n 1: the brush (small trees and bushes and ferns etc.) growing
         beneath taller trees in a wood or forest [syn:
         underbrush, undergrowth, underwood]

U.S. Gazetteer Places (2000):

Underwood-Petersville, AL -- U.S. Census Designated Place in Alabama
   Population (2000):    3137
   Housing Units (2000): 1378
   Land area (2000):     6.026789 sq. miles (15.609310 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    6.026789 sq. miles (15.609310 sq. km)
   FIPS code:            77580
   Located within:       Alabama (AL), FIPS 01
   Location:             34.872469 N, 87.692776 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Underwood-Petersville, AL
    Underwood-Petersville
    Underwood, AL
    Underwood


U.S. Gazetteer Places (2000):

Underwood, ND -- U.S. city in North Dakota
   Population (2000):    812
   Housing Units (2000): 381
   Land area (2000):     0.891559 sq. miles (2.309127 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.891559 sq. miles (2.309127 sq. km)
   FIPS code:            80660
   Located within:       North Dakota (ND), FIPS 38
   Location:             47.456080 N, 101.139601 W
   ZIP Codes (1990):     58576
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Underwood, ND
    Underwood


U.S. Gazetteer Places (2000):

Underwood, IA -- U.S. city in Iowa
   Population (2000):    688
   Housing Units (2000): 266
   Land area (2000):     0.364638 sq. miles (0.944409 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.364638 sq. miles (0.944409 sq. km)
   FIPS code:            79500
   Located within:       Iowa (IA), FIPS 19
   Location:             41.386944 N, 95.678584 W
   ZIP Codes (1990):     51576
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Underwood, IA
    Underwood


U.S. Gazetteer Places (2000):

Underwood, MN -- U.S. city in Minnesota
   Population (2000):    319
   Housing Units (2000): 154
   Land area (2000):     0.424047 sq. miles (1.098277 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.424047 sq. miles (1.098277 sq. km)
   FIPS code:            66172
   Located within:       Minnesota (MN), FIPS 27
   Location:             46.285174 N, 95.870714 W
   ZIP Codes (1990):     56586
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Underwood, MN
    Underwood