The Collaborative International Dictionary of English v.0.48:

Spearmint \Spear"mint`\, n. [So named from its spiry, not
   capitate, inflorescence. --Dr. Prior.] (Bot.)
   A species of mint (Mentha viridis) growing in moist soil.
   It vields an aromatic oil. See Mint, and Mentha.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mint \Mint\ (m[i^]nt), n. [AS. minte, fr. L. mentha, Gr. mi`nqa,
   mi`nqh.] (Bot.)
   The name of several aromatic labiate plants, mostly of the
   genus Mentha, yielding odoriferous essential oils by
   distillation. See Mentha.
   [1913 Webster]

   Note:

   Corn mint is Mentha arvensis.

   Horsemint is Mentha sylvestris, and in the United States
      Monarda punctata, which differs from the true mints in
      several respects.

   Mountain mint is any species of the related genus
      Pycnanthemum, common in North America.

   Peppermint is Mentha piperita.

   Spearmint is Mentha viridis.

   Water mint is Mentha aquatica.
      [1913 Webster]

   Mint camphor. (Chem.) See Menthol.

   Mint julep. See Julep.

   Mint sauce, a sauce flavored with spearmint, for meats.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spearmint
    n 1: common garden herb having clusters of small purplish
         flowers and yielding an oil used as a flavoring [syn:
         spearmint, Mentha spicata]