The Collaborative International Dictionary of English v.0.48:

Proportionate \Pro*por"tion*ate\, a. [L. proportionatus. See
   Proportion.]
   Adjusted to something else according to a proportion;
   proportional. --Longfellow.
   [1913 Webster]

         What is proportionate to his transgression. --Locke.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Proportionate \Pro*por"tion*ate\, v. t. [imp. & p. p.
   Proportionated; p. pr. & vb. n. Proportionating.] [Cf.
   Proportion, v.]
   To make proportional; to adjust according to a settled rate,
   or to due comparative relation; to proportion; as, to
   proportionate punishment to crimes.
   [1913 Webster]

WordNet (r) 3.0 (2006):

proportionate
    adj 1: being in due proportion; "proportionate representation of
           a minority group" [ant: disproportional,
           disproportionate]
    2: agreeing in amount, magnitude, or degree
    3: exhibiting equivalence or correspondence among constituents
       of an entity or between different entities [syn:
       harmonious, proportionate, symmetrical]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "proportionate":
   accordant, adequate, affinitive, affirmative, agreeable, agreeing,
   alike, ample, answerable, appertaining, associative, at one,
   at par, au pair, barely sufficient, coexistent, coexisting,
   coherent, coincident, coinciding, commensurate, comparable,
   comparative, compatible, competent, concordant, concurring,
   conformable, congenial, congruent, congruous, connective,
   consentaneous, consentient, consistent, consonant, cooperating,
   cooperative, correlative, correspondent, corresponding, decent,
   distributional, distributive, drawn, due, en rapport, enough,
   equal, equal to, equalized, equivalent, even, even stephen,
   fifty-fifty, fit, good, good enough, half, half-and-half, halvers,
   harmonious, in accord, in agreement, in rapport, in sync,
   in synchronization, inaccordance, inharmony, knotted, level, like,
   like-minded, linking, minimal, minimum, nip and tuck, of a piece,
   of like mind, of one mind, on a footing, on a level, on a par,
   on all fours, on even ground, par, particular, per capita,
   per head, pertaining, pertinent, plenty, plenty good enough,
   positive, pro rata, proportionable, proportional, prorated, quits,
   reconcilable, referable, referring, relating, relational, relative,
   respective, satisfactory, satisfying, self-consistent, several,
   square, stalemated, substantial, sufficient, sufficient for,
   sufficing, suitable, symbiotic, sympathetic, synchronized,
   synchronous, tied, unanimous, uniform, unisonant, unisonous,
   up to