The Collaborative International Dictionary of English v.0.48:

Misadventure \Mis`ad*ven"ture\ (?; 135), n. [OE. mesaventure, F.
   m['e]saventure.]
   Mischance; misfortune; ill luck; unlucky accident; ill
   adventure. --Chaucer.
   [1913 Webster]

   Homicide by misadventure (Law), homicide which occurs when
      a man, doing a lawful act, without any intention of
      injury, unfortunately kills another; -- called also
      excusable homicide. See Homicide. --Blackstone.
      [1913 Webster]

   Syn: Mischance; mishap; misfortune; disaster; calamity.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "misadventure":
   accident, blow, blunder, boner, bull, calamity, casualty,
   cataclysm, catastrophe, collision, contretemps, crack-up, crash,
   disaster, error, faux pas, grief, howler, ill hap, lapse,
   mischance, misfortune, mishap, nasty blow, pileup, shipwreck,
   shock, slip, smash, smashup, staggering blow, tragedy, wreck