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:

molecular formula \mo*lec"u*lar form"u*la\, n. (Chem.)
   An expression representing the composition of elements in a
   chemical substance, commonly consisting of a series of
   letters and numbers comprising the atomic symbols of each
   element present in a compound followed by the number of atoms
   of that element present in one molecule of the substance.
   Thus the molecular formula for common alcohol (ethyl alcohol)
   is C2H6O, meaning that each molecule contains two carbon
   atoms, six hydrogen atoms, and one oxygen atom. The molecular
   formula may be written to provide some indication of the
   actual structure of the molecule, in which case structural
   units may be written separately. Thus, ethyl alcohol can also
   be written as CH3.CH2.OH or CH3-CH2-OH, in which the
   period or dash between functional groups indicates a single
   bond between the principle atoms of each group. This formula
   shows that in ethyl alcohol, the carbon of a methyl group
   (CH3-) is attached to the carbon of a methylene group
   (-CH2-), which is attached to the oxygen of a hydroxyl
   group (-OH). A structural formula is a graphical
   depiction of the relative positions of atoms in a molecule,
   and may be very complicated.
   [PJC]

WordNet (r) 3.0 (2006):

molecular formula
    n 1: a chemical formula based on analysis and molecular weight