The Collaborative International Dictionary of English v.0.48:

Logarithmic \Log`a*rith"mic\, Logarithmical \Log`a*rith"mic*al\,
   a. [Cf. F. logarithmique.]
   1. Of or pertaining to logarithms; consisting of logarithms.
      [1913 Webster]

   2. Using logarithms; as, logarithmic graph paper; a
      logarithmic scale.
      [PJC]

   3. Having a logarithm in one or more of the unknowns; -- of
      an equation.
      [PJC]

   Logarithmic curve (Math.), a curve which, referred to a
      system of rectangular coordinate axes, is such that the
      ordinate of any point will be the logarithm of its
      abscissa.

   Logarithmic spiral, a spiral curve such that radii drawn
      from its pole or eye at equal angles with each other are
      in continual proportion. See Spiral.
      [1913 Webster]

WordNet (r) 3.0 (2006):

logarithmic
    adj 1: of or relating to or using logarithms; "logarithmic
           function"

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "logarithmic":
   algorismic, algorithmic, aliquot, cardinal, decimal, differential,
   digital, even, exponential, figural, figurate, figurative, finite,
   fractional, imaginary, impair, impossible, infinite, integral,
   irrational, logometric, negative, numeral, numerary, numerative,
   numeric, odd, ordinal, pair, positive, possible, prime, radical,
   rational, real, reciprocal, submultiple, surd, transcendental