Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

   2. (Com.) Hazard of loss; liabillity to loss in property.

   {To run a risk}, to incur hazard; to encounter danger.

   Syn: Danger; hazard; peril; jeopardy; exposure. See {Danger}.

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.

   2. To incur the risk or danger of; as, to risk a battle.

   Syn: To hazard; peril; endanger; jeopard.

Source : WordNet®

risk
     n 1: a source of danger; a possibility of incurring loss or
          misfortune; "drinking alcohol is a health hazard" [syn:
          {hazard}, {jeopardy}, {peril}]
     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: {peril},
         {danger}]
     3: the probability of becoming infected given that exposure to
        an infectious agent has occurred [syn: {risk of infection}]
     4: the probability of being exposed to an infectious agent
        [syn: {risk of exposure}]

risk
     v 1: expose to a chance of loss or damage; "We risked losing a
          lot of money in this venture"; "Why risk your life?"
          [syn: {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},
         {hazard}, {take chances}, {adventure}, {run a risk}, {take
        a chance}]