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.
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   2. (Eccl.) A written confession of faith; a formal statement
      of foctrines.
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   3. (Math.) A rule or principle expressed in algebraic
      language; as, the binominal formula.
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   4. (Med.) A prescription or recipe for the preparation of a
      medicinal compound.
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   5. (Chem.) A symbolic expression (by means of letters,
      figures, etc.) of the constituents or constitution of a
      compound.
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   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.
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   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.
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