The Collaborative International Dictionary of English v.0.48:

Obvious \Ob"vi*ous\, a. [L. obvius; ob (see Ob-) + via way.
   See Voyage.]
   1. Opposing; fronting. [Obs.]
      [1913 Webster]

            To the evil turn
            My obvious breast.                    --Milton.
      [1913 Webster]

   2. Exposed; subject; open; liable. [Obs.] "Obvious to
      dispute." --Milton.
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   3. Easily discovered, seen, or understood; readily perceived
      by the eye or the intellect; plain; evident; apparent; as,
      an obvious meaning; an obvious remark.
      [1913 Webster]

            Apart and easy to be known they lie,
            Amidst the heap, and obvious to the eye. --Pope.
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   Syn: Plain; clear; evident. See Manifest.
        [1913 Webster] -- Ob"vi*ous*ly, adv. --
        Ob"vi*ous-ness, n.
        [1913 Webster] Obvolute

WordNet (r) 3.0 (2006):

obvious
    adj 1: easily perceived by the senses or grasped by the mind;
           "obvious errors" [ant: unobvious]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "obvious":
   apparent, bald, clean-cut, clear, clear as crystal, clear-cut,
   conspicuous, crystal-clear, defined, definite, direct, discernible,
   distinct, evident, explicit, express, glaring, in focus,
   indisputable, indubitable, manifest, noticeable, observable, open,
   open-and-shut, ostensible, overt, palpable, patent, perceivable,
   perceptible, perspicuous, plain, plain as day, prominent,
   pronounced, seeable, self-evident, self-explaining,
   self-explanatory, simple, staring, straightforward, tangible,
   to be seen, unambiguous, unconcealed, undeniable, unequivocal,
   unhidden, unmistakable, unsubtle, visible, well-defined,
   well-marked, well-pronounced, well-resolved