The Collaborative International Dictionary of English v.0.48:

Molecular \Mo*lec"u*lar\, a. [Cf. F. mol['e]culare. See
   Molecule.] (Phys. & Chem.)
   Pertaining to, connected with, produced by, or consisting of,
   molecules; as, molecular forces; molecular groups of atoms,
   etc.
   [1913 Webster]

   Molecular attraction (Phys.), attraction acting between the
      molecules of bodies, and at insensible distances.

   Molecular weight (Chem.), the weight of a molecule of any
      gas or vapor as compared with the hydrogen atom having
      weight of 1 as a standard; the sum of the atomic weights
      of the constituents of a molecule; thus, the molecular
      weight of water (H2O) is 18. For more precise
      measurements, the weight of the carbon isotope carbon-12
      is used as the standard, that isotope having the value of
      12.000. In this systen, now used almost universally, the
      hydrogen atom has a weight of 1.0079.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

molecular weight
    n 1: (chemistry) the sum of the relative atomic masses of the
         constituent atoms of a molecule [syn: molecular weight,
         relative molecular mass]