1. [n]  a wild and exciting undertaking (not necessarily lawful)
2. [v]  take a risk in the hope of a favorable outcome; "When you buy these stocks you are gambling"
3. [v]  put at risk; "I will stake my good reputation for this"

ADVENTURE is a 9 letter word that starts with A.

1. \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.]
   1. That which happens without design; chance; hazard; hap;
      hence, chance of danger or loss.
            Nay, a far less good to man it will be found, if she
            must, at all adventures, be fastened upon him
            individually.                         --Milton.
   2. Risk; danger; peril. [Obs.]
            He was in great adventure of his life. --Berners.
   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.
            He loved excitement and adventure.    --Macaulay.
   4. A remarkable occurrence; a striking event; a stirring
      incident; as, the adventures of one's life. --Bacon.
   5. A mercantile or speculative enterprise of hazard; a
      venture; a shipment by a merchant on his own account.
   {A bill of adventure} (Com.), a writing setting forth that
      the goods shipped are at the owner's risk.
   Syn: Undertaking; enterprise; venture; event.
   

2. \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.
            He would not adventure himself into the theater.
                                                  --Acts xix.
                                                  31.
   2. To venture upon; to run the risk of; to dare.
            Yet they adventured to go back.       --Bunyan,
            Discriminations might be adventured.  --J. Taylor.
   

3. \Ad*ven"ture\, v. i.
   To try the chance; to take the risk.
         I would adventure for such merchandise.  --Shak.