The Collaborative International Dictionary of English v.0.48:

Cautious \Cau"tious\, a. [Cf. L. cautus, fr. caver. See
   Caution.]
   Attentive to examine probable effects and consequences of
   acts with a view to avoid danger or misfortune; prudent;
   circumspect; wary; watchful; as, a cautious general.
   [1913 Webster]

         Cautious feeling for another's pain.     --Byron.
   [1913 Webster]

         Be swift to hear; but cautious of your tongue. --Watts.

   Syn: Wary; watchful; vigilant; prudent; circumspect;
        discreet; heedful; thoughtful; scrupulous; anxious;
        careful.

   Usage: Cautious, Wary, Circumspect. A man is cautious
          who realizes the constant possibility of danger; one
          may be wary, and yet bold and active; a man who is
          circumspect habitually examines things on every side
          in order to weigh and deliberate. It is necessary to
          be cautious at all times; to be wary in cases of
          extraordinary danger; to be circumspect in matters of
          peculiar delicacy and difficulty.
          [1913 Webster]

WordNet (r) 3.0 (2006):

cautious
    adj 1: showing careful forethought; "reserved and cautious;
           never making swift decisions"; "a cautious driver" [ant:
           incautious]
    2: avoiding excess; "a conservative estimate" [syn: cautious,
       conservative]
    n 1: people who are fearful and cautious; "whitewater rafting is
         not for the timid" [syn: timid, cautious] [ant:
         brave]

Moby Thesaurus II by Grady Ward, 1.0:

133 Moby Thesaurus words for "cautious":
   alert, ambling, attentive, cagey, calculating, canny, careful,
   chary, circumspect, claudicant, considerate, cozy, crawling,
   creeping, creeping like snail, curious, deliberate, demurring,
   diffident, discreet, disinclined to believe, disposed to doubt,
   easy, expedient, faltering, flagging, foot-dragging, foresighted,
   forethoughtful, gentle, gingerly, gradual, guarded, halting,
   hard of belief, heedful, hesitant, hesitating, hobbled, hobbling,
   idle, impervious to persuasion, inconvincible, incredulous,
   indolent, jibbing, judicious, languid, languorous, lazy,
   leaving out nothing, leery, leisurely, limping, loving, lumbering,
   mindful, moderate, noncommittal, on guard,
   overlooking no possibility, pawky, poking, poky, politic,
   precautious, provident, prudent, regardful, relaxed, reluctant,
   safe, sauntering, scheming, scrupling, shilly-shallying, shrewd,
   shuffling, shy of belief, skeptical, slack, slothful, slow,
   slow as death, slow as molasses, slow as slow, slow to act,
   slow-crawling, slow-foot, slow-going, slow-legged, slow-moving,
   slow-paced, slow-poky, slow-running, slow-sailing, slow-stepped,
   sluggish, snail-paced, snaillike, solicitous, staggering, sticking,
   stickling, straining, strolling, suspecting, suspicious, tender,
   tentative, thorough, thoughtful, timid, toddling, tortoiselike,
   tottering, trudging, turtlelike, unadventurous, uncommunicative,
   unconvincible, uncredulous, undaring, unenterprising, unhurried,
   unpersuadable, unpersuasible, unprecipitate, unwilling to accept,
   vigilant, waddling, wary, watchful