The Collaborative International Dictionary of English v.0.48:

Formula \For"mu*la\, n.; pl. E. Formulas, L. Formul[ae].
   [L., dim. of forma form, model. SeeForm, 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.
      [1913 Webster]

   2. (Eccl.) A written confession of faith; a formal statement
      of foctrines.
      [1913 Webster]

   3. (Math.) A rule or principle expressed in algebraic
      language; as, the binominal formula.
      [1913 Webster]

   4. (Med.) A prescription or recipe for the preparation of a
      medicinal compound.
      [1913 Webster]

   5. (Chem.) A symbolic expression (by means of letters,
      figures, etc.) of the constituents or constitution of a
      compound.
      [1913 Webster]

   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.
         [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            In philosophical language, the term empirical means
            simply what belongs to or is the product of
            experience or observation.            --Sir W.
                                                  Hamilton.
      [1913 Webster]

            The village carpenter . . . lays out his work by
            empirical rules learnt in his apprenticeship. --H.
                                                  Spencer.
      [1913 Webster]

   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.
      [1913 Webster]

   Empirical formula. (Chem.) See under Formula.

   Syn: See Transcendental.
        [1913 Webster]

WordNet (r) 3.0 (2006):

empirical formula
    n 1: a chemical formula showing the ratio of elements in a
         compound rather than the total number of atoms