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]