The Collaborative International Dictionary of English v.0.48:

Manna \Man"na\ (m[a^]n"n[.a]), n. [L., fr. Gr. ma`nna, Heb.
   m[=a]n; cf. Ar. mann, properly, gift (of heaven).]
   1. (Script.) The food supplied to the Israelites in their
      journey through the wilderness of Arabia; hence, divinely
      supplied food. --Ex. xvi. 15.
      [1913 Webster]

   2. (Bot.) A name given to lichens of the genus Lecanora,
      sometimes blown into heaps in the deserts of Arabia and
      Africa, and gathered and used as food; called also manna
      lichen.
      [1913 Webster]

   3. (Bot. & Med.) A sweetish exudation in the form of pale
      yellow friable flakes, coming from several trees and
      shrubs and used in medicine as a gentle laxative, as the
      secretion of Fraxinus Ornus, and Fraxinus
      rotundifolia, the manna ashes of Southern Europe.
      [1913 Webster]

   Note: Persian manna is the secretion of the camel's thorn
         (see Camel's thorn, under Camel); Tamarisk manna,
         that of the Tamarisk mannifera, a shrub of Western
         Asia; Australian, manna, that of certain species of
         eucalyptus; Brian[,c]on manna, that of the European
         larch.
         [1913 Webster]

   Manna insect (Zool), a scale insect (Gossyparia
      mannipara), which causes the exudation of manna from the
      Tamarix tree in Arabia.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

manna ash \manna ash\ n. (Bot.),
   A South Mediterranean ash (Fraxinus ornus) having fragrant
   white flowers in dense panicles and yielding manna.

   Syn: flowering ash, Fraxinus ornus.
        [WordNet 1.5]

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]

WordNet (r) 3.0 (2006):

Fraxinus ornus
    n 1: southern Mediterranean ash having fragrant white flowers in
         dense panicles and yielding manna [syn: manna ash,
         flowering ash, Fraxinus ornus]