The Collaborative International Dictionary of English v.0.48:

Wintergreen \Win"ter*green`\, n. (Bot.)
   A plant which keeps its leaves green through the winter.
   [1913 Webster]

   Note: In England, the name wintergreen is applied to the
         species of Pyrola which in America are called
         English wintergreen, and shin leaf (see Shin leaf,
         under Shin.) In America, the name wintergreen is
         given to Gaultheria procumbens, a low evergreen
         aromatic plant with oval leaves clustered at the top of
         a short stem, and bearing small white flowers followed
         by red berries; -- called also checkerberry, and
         sometimes, though improperly, partridge berry.
         [1913 Webster]

   Chickweed wintergreen, a low perennial primulaceous herb
      (Trientalis Americana); -- also called star flower.

   Flowering wintergreen, a low plant (Polygala paucifolia)
      with leaves somewhat like those of the wintergreen
      (Gaultheria), and bearing a few showy, rose-purple
      blossoms.

   oil of wintergreen, An aromatic oil, consisting almost
      entirely of methyl salicylate (CH3CO.O.C6H4.OH),
      obtained by distillation of an extract of the wintergreen
      (Gaultheria procumbens); it can also be obtained from
      some other plants. It is used as a flavoring agent for
      tooth powders and pastes, sometimes combined with menthol
      or eucalyptus. It is called also oil of teaberry, oil
      of partridgeberry, and oil of gaultheria.

   Spotted wintergreen, a low evergreen plant (Chimaphila
      maculata) with ovate, white-spotted leaves.
      [1913 Webster + PJC]

WordNet (r) 3.0 (2006):

wintergreen
    n 1: any of several evergreen perennials of the genus Pyrola
         [syn: wintergreen, pyrola]
    2: creeping shrub of eastern North America having white bell-
       shaped flowers followed by spicy red berrylike fruit and
       shiny aromatic leaves that yield wintergreen oil [syn:
       teaberry, wintergreen, checkerberry, mountain tea,
       groundberry, ground-berry, creeping wintergreen,
       Gaultheria procumbens]
    3: spicy red berrylike fruit; source of wintergreen oil [syn:
       wintergreen, boxberry, checkerberry, teaberry,
       spiceberry]