The Collaborative International Dictionary of English v.0.48:

Boxberry \Box"ber`ry\, n. (Bot.)
   The wintergreen. (Gaultheria procumbens). [Local, U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

boxberry
    n 1: creeping woody plant of eastern North America with shiny
         evergreen leaves and scarlet berries [syn:
         partridgeberry, boxberry, twinberry, Mitchella
         repens]
    2: spicy red berrylike fruit; source of wintergreen oil [syn:
       wintergreen, boxberry, checkerberry, teaberry,
       spiceberry]