The Collaborative International Dictionary of English v.0.48:

Mannite \Man"nite\, n.
   1. Same as mannitol.
      [PJC]

   2. (Bot.) A sweet white efflorescence from dried fronds of
      kelp, especially from those of the Laminaria saccharina,
      or devil's apron.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

mannitol \man"ni*tol\, n. [Mannite + -ol.]
   1. (Chem.) A white crystalline hexose
      (HO.CH2.(CHOH)4.CH2.OH) of a sweet taste obtained from a
      so-called manna, the dried sap of the flowering ash
      (Fraxinus ornus); -- called also mannite, and hydroxy
      hexane. Cf. Dulcite. It is used in pharmacy as
      excipient and diluent for solids and liquids. It is also
      used as a food additive for anti-caking properties, or as
      a sweetener, and, illegally, to "cut" (dilute) illegal
      drugs such as cocaine or heroin.

   Syn: D-mannitol; manna sugar; cordycepic acid; Diosmol;
        Mannicol; Mannidex; Osmiktrol; Osmosal.
        [1913 Webster +PJC]