The Collaborative International Dictionary of English v.0.48:

Dorsal \Dor"sal\, a. [F. dorsal, LL. dorsalis, fr. L. dorsualis,
   fr. dorsum back; cf. Gr. ?, ?, mountain ridge. Cf. Dorse,
   Dorsel, Dosel.]
   1. (Anat.) Pertaining to, or situated near, the back, or
      dorsum, of an animal or of one of its parts; notal;
      tergal; neural; as, the dorsal fin of a fish; the dorsal
      artery of the tongue; -- opposed to ventral.
      [1913 Webster]

   2. (Bot.)
      (a) Pertaining to the surface naturally inferior, as of a
          leaf.
      (b) Pertaining to the surface naturally superior, as of a
          creeping hepatic moss.
          [1913 Webster]

   Dorsal vessel (Zool.), a central pulsating blood vessel
      along the back of insects, acting as a heart.
      [1913 Webster]