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
    adj 1: relating to or produced by or consisting of molecules;
           "molecular structure"; "molecular oxygen"; "molecular
           weight is the sum of all the atoms in a molecule"
    2: relating to simple or elementary organization; "proceed by
       more and more detailed analysis to the molecular facts of
       perception"--G.A. Miller [ant: molar(a)]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "molecular":
   atomic, corpuscular, embryonic, evanescent, germinal, granular,
   impalpable, imperceptible, imponderable, inappreciable,
   indiscernible, infinitesimal, intangible, invisible, microcosmic,
   microscopic, subatomic, tenuous, thin, ultramicroscopic,
   unseeable