The Collaborative International Dictionary of English v.0.48:

Adventure \Ad*ven"ture\ (?; 135), n. [OE. aventure, aunter,
   anter, F. aventure, fr. LL. adventura, fr. L. advenire,
   adventum, to arrive, which in the Romance languages took the
   sense of "to happen, befall." See Advene.]
   [1913 Webster]
   1. That which happens without design; chance; hazard; hap;
      hence, chance of danger or loss.
      [1913 Webster]

            Nay, a far less good to man it will be found, if she
            must, at all adventures, be fastened upon him
            individually.                         --Milton.
      [1913 Webster]

   2. Risk; danger; peril. [Obs.]
      [1913 Webster]

            He was in great adventure of his life. --Berners.
      [1913 Webster]

   3. The encountering of risks; hazardous and striking
      enterprise; a bold undertaking, in which hazards are to be
      encountered, and the issue is staked upon unforeseen
      events; a daring feat.
      [1913 Webster]

            He loved excitement and adventure.    --Macaulay.
      [1913 Webster]

   4. A remarkable occurrence; a striking event; a stirring
      incident; as, the adventures of one's life. --Bacon.
      [1913 Webster]

   5. A mercantile or speculative enterprise of hazard; a
      venture; a shipment by a merchant on his own account.
      [1913 Webster]

   A bill of adventure (Com.), a writing setting forth that
      the goods shipped are at the owner's risk.
      [1913 Webster]

   Syn: Undertaking; enterprise; venture; event.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Adventure \Ad*ven"ture\, v. t. [imp. & p. p. Adventured; p.
   pr. & vb. n. Adventuring.] [OE. aventuren, auntren, F.
   aventurer, fr. aventure. See Adventure, n.]
   1. To risk, or hazard; jeopard; to venture.
      [1913 Webster]

            He would not adventure himself into the theater.
                                                  --Acts xix.
                                                  31.
      [1913 Webster]

   2. To venture upon; to run the risk of; to dare.
      [1913 Webster]

            Yet they adventured to go back.       --Bunyan,
      [1913 Webster]

            Discriminations might be adventured.  --J. Taylor.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Adventure \Ad*ven"ture\, v. i.
   To try the chance; to take the risk.
   [1913 Webster]

         I would adventure for such merchandise.  --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

adventure
    n 1: a wild and exciting undertaking (not necessarily lawful)
         [syn: adventure, escapade, risky venture, dangerous
         undertaking]
    v 1: 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]
    2: put at risk; "I will stake my good reputation for this" [syn:
       venture, hazard, adventure, stake, jeopardize]