The Collaborative International Dictionary of English v.0.48:

Rectify \Rec"ti*fy\ (-f?), v. t. [imp. & p. p. Rectified
   (-f?d); p. pr. & vb. n. Rectifying (-f?`?ng).] [F.
   rectifier, LL. rectificare; L. rectus right + -ficare (in
   comp.) to make. See Right, and -fy.]
   1. To make or set right; to correct from a wrong, erroneous,
      or false state; to amend; as, to rectify errors, mistakes,
      or abuses; to rectify the will, the judgment, opinions; to
      rectify disorders.
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            I meant to rectify my conscience.     --Shak.
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            This was an error of opinion which a conflicting
            opinion would have rectified.         --Burke.
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   2. (Chem.) To refine or purify by repeated distillation or
      sublimation, by which the fine parts of a substance are
      separated from the grosser; as, to rectify spirit of wine.
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   3. (Com.) To produce ( as factitious gin or brandy) by
      redistilling low wines or ardent spirits (whisky, rum,
      etc.), flavoring substances, etc., being added.
      [1913 Webster]
      [1913 Webster]

   To rectify a globe, to adjust it in order to prepare for
      the solution of a proposed problem.
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   Syn: To amend; emend; correct; better; mend; reform; redress;
        adjust; regulate; improve. See Amend.
        [1913 Webster] Rectilineal

WordNet (r) 3.0 (2006):

rectify
    v 1: math: determine the length of; "rectify a curve"
    2: reduce to a fine, unmixed, or pure state; separate from
       extraneous matter or cleanse from impurities; "refine sugar"
       [syn: refine, rectify]
    3: bring, lead, or force to abandon a wrong or evil course of
       life, conduct, and adopt a right one; "The Church reformed
       me"; "reform your conduct" [syn: reform, reclaim,
       regenerate, rectify]
    4: set straight or right; "remedy these deficiencies"; "rectify
       the inequities in salaries"; "repair an oversight" [syn:
       rectify, remediate, remedy, repair, amend]
    5: make right or correct; "Correct the mistakes"; "rectify the
       calculation" [syn: correct, rectify, right] [ant:
       falsify]
    6: convert into direct current; "rectify alternating current"

Moby Thesaurus II by Grady Ward, 1.0:

152 Moby Thesaurus words for "rectify":
   accommodate, accommodate with, accord, adapt, adapt to, adjust,
   adjust to, agree with, ameliorate, amend, assimilate,
   assimilate to, atone, attune, be guided by, bend, blue-pencil,
   bolt, chime in with, clarify, clear, compensate, comply,
   comply with, compose, conform, coordinate, correct, correspond,
   cover, cure, cut to, decrassify, depurate, discipline, disentangle,
   distill, do penance, edit, edulcorate, elute, emend, emendate,
   equalize, essentialize, expiate, extend, extract, fall in with,
   fill up, filter, filtrate, fit, fix, flatten, follow, gear to,
   give and take, give satisfaction, go by, harmonize, homologate,
   homologize, improve, indemnify, key to, leach, lixiviate,
   make all square, make amends, make compensation, make conform,
   make good, make plumb, make right, make uniform, make up for,
   measure, meet, mend, mold, observe, pay back, pay reparations,
   percolate, proportion, purify, put in tune, put right,
   put straight, put to rights, rebuild, recense, recompense,
   reconcile, redact, redraft, redress, refine, regulate, remedy,
   remunerate, repair, repay, requite, retaliate, revamp, revise,
   rework, rewrite, right, rub off corners, screen, separate, set,
   set right, set straight, set to rights, set up, settle, shape,
   sieve, sift, similarize, sit up, smooth, spiritualize, square,
   stand up, straighten, straighten out, straighten up, strain,
   sublimate, sublime, suit, sync, synchronize, tailor, tally with,
   trim to, true, true up, try, tune, unbend, uncurl, unkink, unsnarl,
   winnow, work over, yield