The Collaborative International Dictionary of English v.0.48:

Cowberry \Cow"ber`ry\ (-b[e^]r`r[y^]), n.; pl. Cowberries
   (-r[i^]z). (Bot.)
   A species of Vaccinium (Vaccinium Vitis-id[ae]a), which
   bears acid red berries which are sometimes used in cookery;
   -- locally called mountain cranberry.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cowberry
    n 1: low evergreen shrub of high north temperate regions of
         Europe and Asia and America bearing red edible berries
         [syn: cowberry, mountain cranberry, lingonberry,
         lingenberry, lingberry, foxberry, Vaccinium vitis-
         idaea]
    2: tart red berries similar to American cranberries but smaller
       [syn: lingonberry, mountain cranberry, cowberry,
       lowbush cranberry]