Source : Webster's Revised Unabridged Dictionary (1913)

Diet \Di"et\, n. Specifically:
   Any of various national or local assemblies; as,
   (a) Occasionally, the Reichstag of the German Empire,
       Reichsrath of the Austrian Empire, the federal
       legislature of Switzerland, etc.
   (b) The legislature of Denmark, Sweden, Japan, or Hungary.
   (c) The state assembly or any of various local assemblies in
       the states of the German Empire, as the legislature
       (Landtag) of the kingdom of Prussia, and the Diet of the
       Circle (Kreistag) in its local government.
   (d) The local legislature (Landtag) of an Austrian province.
   (e) The federative assembly of the old Germanic Confederation
       (1815 -- 66).
   (f) In the old German or Holy Roman Empire, the great formal
       assembly of counselors (the Imperial Diet or Reichstag)
       or a small, local, or informal assembly of a similar kind
       (the Court Diet, or Hoftag).

   Note: The most celebrated Imperial Diets are the three
         following, all held under Charles V.:

   {Diet of Worms}, 1521, the object of which was to check the
      Reformation and which condemned Luther as a heretic;

   {D. of Spires, or Speyer}, 1529, which had the same object
      and issued an edict against the further dissemination of
      the new doctrines, against which edict Lutheran princes
      and deputies protested (hence Protestants):

   {D. of Augsburg}, 1530, the object of which was the
      settlement of religious disputes, and at which the
      Augsburg Confession was presented but was denounced by the
      emperor, who put its adherents under the imperial ban.

Diet \Di"et\, v. i.
   1. To eat; to take one's meals. [Obs.]

            Let him . . . diet in such places, where there is
            good company of the nation, where he traveleth.
                                                  --Bacon.

   2. To eat according to prescribed rules; to ear sparingly;
      as, the doctor says he must diet.

Diet \Di"et\, n. [F. di[`e]te, LL. dieta, diaeta, an assembly, a
   day's journey; the same word as diet course of living, but
   with the sense changed by L. dies day: cf. G. tag day? and
   {Reichstag}.]
   A legislative or administrative assembly in Germany, Poland,
   and some other countries of Europe; a deliberative
   convention; a council; as, the Diet of Worms, held in 1521.

Diet \Di"et\, n. [F. di[`e]te, L. diaeta, fr. Gr. ? manner of
   living.]
   1. Course of living or nourishment; what is eaten and drunk
      habitually; food; victuals; fare. ``No inconvenient
      diet.'' --Milton.

   2. A course of food selected with reference to a particular
      state of health; prescribed allowance of food; regimen
      prescribed.

            To fast like one that takes diet.     --Shak.

   {Diet kitchen}, a kitchen in which diet is prepared for
      invalids; a charitable establishment that provides proper
      food for the sick poor.

Diet \Di"et\, v. t. [imp. & p. p. {Dieted}; p. pr. & vb. n.
   {Dieting}.]
   1. To cause to take food; to feed. [R.] --Shak.

   2. To cause to eat and drink sparingly, or by prescribed
      rules; to regulate medicinally the food of.

            She diets him with fasting every day. --Spenser.

Source : WordNet®

diet
     v 1: follow a regimen or a diet, as for health reasons; "He has
          high blood pressure and must stick to a low-salt diet"
     2: eat sparingly, for health reasons or to lose weight

diet
     n 1: a prescribed selection of foods
     2: a legislative assembly in certain countries (e.g., Japan)
     3: the usual food and drink consumed by an organism (person or
        animal)
     4: the act of restricting your food intake (or your intake of
        particular foods) [syn: {dieting}]