The Collaborative International Dictionary of English v.0.48:

Aventure \A*ven"ture\ (?; 135), n. [See Adventure, n.]
   1. Accident; chance; adventure. [Obs.] --Chaucer.
      [1913 Webster]

   2. (Old Law) A mischance causing a person's death without
      felony, as by drowning, or falling into the fire.
      [1913 Webster]