The Collaborative International Dictionary of English v.0.48:

Approximate \Ap*prox"i*mate\, v. t. [imp. & p. p.
   Approximated; p. pr. & vb. n. Approximating.]
   1. To carry or advance near; to cause to approach.
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            To approximate the inequality of riches to the level
            of nature.                            --Burke.
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   2. To come near to; to approach.
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            The telescope approximates perfection. --J. Morse.
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The Collaborative International Dictionary of English v.0.48:

Approximate \Ap*prox"i*mate\, v. i.
   To draw; to approach.
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The Collaborative International Dictionary of English v.0.48:

Approximate \Ap*prox"i*mate\, a. [L. approximatus, p. p. of
   approximare to approach; ad + proximare to come near. See
   Proximate.]
   1. Approaching; proximate; nearly resembling.
      [1913 Webster]

   2. Near correctness; nearly exact; not perfectly accurate;
      as, approximate results or values.
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   Approximate quantities (Math.), those which are nearly, but
      not, equal.
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WordNet (r) 3.0 (2006):

approximate
    adj 1: not quite exact or correct; "the approximate time was 10
           o'clock"; "a rough guess"; "a ballpark estimate" [syn:
           approximate, approximative, rough]
    2: very close in resemblance; "sketched in an approximate
       likeness"; "a near likeness" [syn: approximate, near]
    3: located close together; "with heads close together";
       "approximate leaves grow together but are not united" [syn:
       approximate, close together(p)]
    v 1: be close or similar; "Her results approximate my own" [syn:
         approximate, come close]
    2: judge tentatively or form an estimate of (quantities or
       time); "I estimate this chicken to weigh three pounds" [syn:
       estimate, gauge, approximate, guess, judge]

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "approximate":
   accost, advance, advancing, ape, appear like, approach,
   approaching, appropinquate, approximating, approximative,
   arm-in-arm, assimilate, attracted to, be around, be like, be near,
   be redolent of, bear down on, bear down upon, bear resemblance,
   bear up, begin to, bring near, bring to mind, burning, call,
   call to mind, call up, cheek-by-jowl, close, close in, close with,
   come, come close, come closer, come forward, come near, come on,
   come up, coming, comparable, compare with, confront, connaturalize,
   copy, correspond, counterfeit, draw near, draw nigh, drawn to,
   encounter, estimated, evoke, favor, follow, forthcoming, gain upon,
   get warm, hand-in-hand, homologous, hot, imitate, imminent,
   imprecise, inaccurate, incorrect, inexact, intimate, judge, lax,
   like, look like, loose, match, mimic, mirror, much at one,
   much the same, narrow the gap, near, near the mark, nearing,
   nearish, nearly reproduce, nearly the same, negligent, nigh,
   nighish, not tell apart, oncoming, out of line, out of plumb,
   out of square, out of true, parallel, partake of, place, propinque,
   proximal, proximate, put, quasi, reckon, relatable, relative,
   remind one of, resemble, rough, rude, same but different, savor of,
   seem like, side-by-side, sidle up to, similar, similarize,
   simulate, smack of, sound like, stack up with, step up, suggest,
   take after, to come, unfactual, unprecise, unrigorous, upcoming,
   verge on, vicinal, warm