The Collaborative International Dictionary of English v.0.48:

Guard \Guard\, v. t. [imp. & p. p. Guarded; p. pr. & vb. n.
   Gurding.] [OF. guarder, garder, warder, F. garder, fr. OHG.
   wart?n to be on the watch, await, G. marten. See Ward, v. &
   n., and cf. Guard, n.]
   1. To protect from danger; to secure against surprise,
      attack, or injury; to keep in safety; to defend; to
      shelter; to shield from surprise or attack; to protect by
      attendance; to accompany for protection; to care for.
      [1913 Webster]

            For Heaven still guards the right.    --Shak.
      [1913 Webster]

   2. To keep watch over, in order to prevent escape or restrain
      from acts of violence, or the like.
      [1913 Webster]

   3. To protect the edge of, esp. with an ornamental border;
      hence, to face or ornament with lists, laces, etc.

            The body of your discourse is sometime guarded with
            fragments, and the guards are but slightly basted on
            neither.                              --Shak.
      [1913 Webster]

   4. To fasten by binding; to gird. [Obs.] --B. Jonson.

   Syn: To defend; protect; shield; keep; watch.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Guarded \Guard"ed\, a.
   Cautious; wary; circumspect; as, he was guarded in his
   expressions; framed or uttered with caution; as, his
   expressions were guarded. -- Guard"edly, adv. --
   Guard"ed*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

guarded
    adj 1: prudent; "guarded optimism" [syn: guarded,
           restrained]

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "guarded":
   Argus-eyed, Olympian, all ears, all eyes, aloof, apprehensive,
   armed, arrested, aux aguets, backward, bashful, blank, bridled,
   buried, cagey, calculating, canny, careful, cautious, chary,
   chilled, chilly, circumspect, cloaked, cold, concealed,
   considerate, constrained, controlled, cool, copyrighted, covered,
   covert, curbed, custodial, defended, deliberate, detached,
   discreet, disinclined to believe, disposed to doubt, distant,
   eagle-eyed, expressionless, forbidding, frigid, frosty, gingerly,
   hard of belief, hawk-eyed, heedful, hesitant, hidden, icy,
   impassive, impersonal, impervious to persuasion, in check,
   in leading strings, in remission, inaccessible, inconvincible,
   incredulous, inhibited, introverted, invulnerable, judicious,
   keen-eyed, leaving out nothing, leery, lidless, loath, mindful,
   modest, noncommittal, obscured, observant, offish, on guard,
   on leash, on the lookout, on the watch, open-eyed,
   overlooking no possibility, patented, pawky, pent-up, policed,
   politic, privy, protected, prudent, regardful, reluctant, remote,
   removed, repressed, reserved, restrained, retarded, reticent,
   retiring, safe, safeguarded, screened, sharp-eyed, sheltered,
   shielded, shrinking, shrouded, shy of belief, skeptical, sleepless,
   slow to act, slowed down, standoff, standoffish, subdued,
   suppressed, suspecting, suspicious, tentative, thorough,
   unadventurous, unaffable, unapproachable, uncommunicative,
   uncongenial, unconvincible, uncredulous, undaring, undemonstrative,
   under control, under discipline, under restraint, unenterprising,
   unexpansive, ungenial, unpersuadable, unpersuasible, unprecipitate,
   unwilling to accept, vigilant, wary, watchful, with open eyes,
   withdrawn