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]

WordNet (r) 3.0 (2006):

manna
    n 1: hardened sugary exudation of various trees
    2: (Old Testament) food that God gave the Israelites during the
       Exodus [syn: miraculous food, manna, manna from heaven]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "manna":
   TLC, ambrosia, benefaction, benefit, benevolence, blessing,
   bonne bouche, boon, bread, care, cate, choice morsel, daily bread,
   dainty, delicacy, dessert, economic support, endowment, favor,
   godsend, goody, grace, keep, kickshaw, livelihood, living,
   loaves and fishes, maintenance, manna from heaven, meat, morsel,
   mothering, nectar, nourishment, nurture, price support, provision,
   savory, subsidization, subsidy, subsistence, subvention, support,
   sustainment, sustenance, sustentation, tender loving care, tidbit,
   titbit, treat, upkeep



Easton's 1897 Bible Dictionary:

Manna
   Heb. man-hu, "What is that?" the name given by the Israelites to
   the food miraculously supplied to them during their wanderings
   in the wilderness (Ex. 16:15-35). The name is commonly taken as
   derived from _man_, an expression of surprise, "What is it?" but
   more probably it is derived from _manan_, meaning "to allot,"
   and hence denoting an "allotment" or a "gift." This "gift" from
   God is described as "a small round thing," like the "hoar-frost
   on the ground," and "like coriander seed," "of the colour of
   bdellium," and in taste "like wafers made with honey." It was
   capable of being baked and boiled, ground in mills, or beaten in
   a mortar (Ex. 16:23; Num. 11:7). If any was kept over till the
   following morning, it became corrupt with worms; but as on the
   Sabbath none fell, on the preceding day a double portion was
   given, and that could be kept over to supply the wants of the
   Sabbath without becoming corrupt. Directions concerning the
   gathering of it are fully given (Ex. 16:16-18, 33; Deut. 8:3,
   16). It fell for the first time after the eighth encampment in
   the desert of Sin, and was daily furnished, except on the
   Sabbath, for all the years of the wanderings, till they encamped
   at Gilgal, after crossing the Jordan, when it suddenly ceased,
   and where they "did eat of the old corn of the land; neither had
   the children of Israel manna any more" (Josh. 5:12). They now no
   longer needed the "bread of the wilderness."

     This manna was evidently altogether a miraculous gift, wholly
   different from any natural product with which we are acquainted,
   and which bears this name. The manna of European commerce comes
   chiefly from Calabria and Sicily. It drops from the twigs of a
   species of ash during the months of June and July. At night it
   is fluid and resembles dew, but in the morning it begins to
   harden. The manna of the Sinaitic peninsula is an exudation from
   the "manna-tamarisk" tree (Tamarix mannifera), the el-tarfah of
   the Arabs. This tree is found at the present day in certain
   well-watered valleys in the peninsula of Sinai. The manna with
   which the people of Israel were fed for forty years differs in
   many particulars from all these natural products.

     Our Lord refers to the manna when he calls himself the "true
   bread from heaven" (John 6:31-35; 48-51). He is also the "hidden
   manna" (Rev. 2:17; comp. John 6:49,51).


The Devil's Dictionary (1881-1906):

MANNA, n.  A food miraculously given to the Israelites in the
wilderness.  When it was no longer supplied to them they settled
down and tilled the soil, fertilizing it, as a rule, with the bodies
of the original occupants.