Source : Webster's Revised Unabridged Dictionary (1913)

Empiric \Em*pir"ic\, Empirical \Em*pir"ic*al\, a.
   1. Pertaining to, or founded upon, experiment or experience;
      depending upon the observation of phenomena; versed in
      experiments.

            In philosophical language, the term empirical means
            simply what belongs to or is the product of
            experience or observation.            --Sir W.
                                                  Hamilton.

            The village carpenter . . . lays out his work by
            empirical rules learnt in his apprenticeship. --H.
                                                  Spencer.

   2. Depending upon experience or observation alone, without
      due regard to science and theory; -- said especially of
      medical practice, remedies, etc.; wanting in science and
      deep insight; as, empiric skill, remedies.

   {Empirical formula}. (Chem.) See under {Formula}.

   Syn: See {Transcendental}.

Formula \For"mu*la\, n.; pl. E. {Formulas}, L. {Formul[ae]}.
   [L., dim. of forma form, model. See{Form}, n.]
   1. A prescribed or set form; an established rule; a fixed or
      conventional method in which anything is to be done,
      arranged, or said.

   2. (Eccl.) A written confession of faith; a formal statement
      of foctrines.

   3. (Math.) A rule or principle expressed in algebraic
      language; as, the binominal formula.

   4. (Med.) A prescription or recipe for the preparation of a
      medicinal compound.

   5. (Chem.) A symbolic expression (by means of letters,
      figures, etc.) of the constituents or constitution of a
      compound.

   Note: Chemical formul[ae] consist of the abbreviations of the
         names of the elements, with a small figure at the lower
         right hand, to denote the number of atoms of each
         element contained.

   {Empirical formula} (Chem.), an expression which gives the
      simple proportion of the constituents; as, the empirical
      formula of acetic acid is {C2H4O2}.

   {Graphic formula}, {Rational formula} (Chem.), an expression
      of the constitution, and in a limited sense of the
      structure, of a compound, by the grouping of its atoms or
      radicals; as, a rational formula of acetic acid is
      {CH3.(C:O).OH}; -- called also {structural formula},
      {constitutional formula}, etc. See also the formula of
      {Benzene nucleus}, under {Benzene}.

   {Molecular formula} (Chem.), a formula indicating the
      supposed molecular constitution of a compound.

Source : WordNet®

empirical formula
     n : a chemical formula showing the ratio of elements in a
         compound rather than the total number of atoms