The Collaborative International Dictionary of English v.0.48:

Risk \Risk\, n. [F. risque; cf. It. risco, risico, rischio, Pg.
   risco, Sp. riesgo, and also Sp. risco a steep rock; all
   probably fr. L. resceare to cut off; pref. re- re- + secare
   to cut; -- the word having been probably first used among
   sailors. See Section.]
   1. Hazard; danger; peril; exposure to loss, injury, or
      destruction.
      [1913 Webster]

            The imminent and constant risk of assassination, a
            risk which has shaken very strong nerves.
                                                  --Macaulay.
      [1913 Webster]

   2. (Com.) Hazard of loss; liabillity to loss in property.
      [1913 Webster]

   To run a risk, to incur hazard; to encounter danger.
      [1913 Webster]

   Syn: Danger; hazard; peril; jeopardy; exposure. See Danger.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Risk \Risk\, v. t. [imp. & p. p. Risked; p. pr. & vb. n.
   Risking.] [CF. F. risquer. See Risk, n.]
   1. To expose to risk, hazard, or peril; to venture; as, to
      risk goods on board of a ship; to risk one's person in
      battle; to risk one's fame by a publication.
      [1913 Webster]

   2. To incur the risk or danger of; as, to risk a battle.
      [1913 Webster]

   Syn: To hazard; peril; endanger; jeopard.
        [1913 Webster]

WordNet (r) 3.0 (2006):

risk
    n 1: a source of danger; a possibility of incurring loss or
         misfortune; "drinking alcohol is a health hazard" [syn:
         hazard, jeopardy, peril, risk, endangerment]
    2: a venture undertaken without regard to possible loss or
       injury; "he saw the rewards but not the risks of crime";
       "there was a danger he would do the wrong thing" [syn:
       risk, peril, danger]
    3: the probability of becoming infected given that exposure to
       an infectious agent has occurred [syn: risk, risk of
       infection]
    4: the probability of being exposed to an infectious agent [syn:
       risk, risk of exposure]
    v 1: expose to a chance of loss or damage; "We risked losing a
         lot of money in this venture"; "Why risk your life?"; "She
         laid her job on the line when she told the boss that he was
         wrong" [syn: risk, put on the line, lay on the line]
    2: take a risk in the hope of a favorable outcome; "When you buy
       these stocks you are gambling" [syn: gamble, chance,
       risk, hazard, take chances, adventure, run a risk,
       take a chance]