The Collaborative International Dictionary of English v.0.48:

Adventurer \Ad*ven"tur*er\, n. [Cf. F. aventurier.]
   [1913 Webster]
   1. One who adventures; as, the merchant adventurers; one who
      seeks his fortune in new and hazardous or perilous
      enterprises.
      [1913 Webster]

   2. A social pretender on the lookout for advancement.
      [1913 Webster]

WordNet (r) 3.0 (2006):

adventurer
    n 1: a person who enjoys taking risks [syn: adventurer,
         venturer]
    2: someone who travels into little known regions (especially for
       some scientific purpose) [syn: explorer, adventurer]