The Collaborative International Dictionary of English v.0.48:

Hazardous \Haz"ard*ous\ (-[u^]s), a. [Cf. F. hasardeux.]
   Exposed to hazard; dangerous; risky.
   [1913 Webster]

         To enterprise so hazardous and high!     --Milton.

   Syn: Perilous; dangerous; bold; daring; adventurous;
        venturesome; precarious; uncertain. -- Haz"ard*ous*ly,
        adv. -- Haz"ard*ous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

hazardous
    adj 1: involving risk or danger; "skydiving is a hazardous
           sport"; "extremely risky going out in the tide and fog";
           "a wild financial scheme" [syn: hazardous, risky,
           wild]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "hazardous":
   adventurous, aleatory, chancy, dangerous, desultory, dicey, dickey,
   fraught with danger, full of risk, hairy, infirm, insecure,
   insubstantial, jeopardous, parlous, perilous, precarious,
   provisional, questionable, riskful, risky, shaky, shifting, shifty,
   slippery, speculative, temporary, tentative, ticklish, treacherous,
   tricky, uncertain, undependable, unfaithworthy, unhealthy,
   unpredictable, unreliable, unsafe, unsolid, unsound, unstable,
   unsteadfast, unsteady, unsubstantial, unsure, untrustworthy,
   venturesome, venturous, wicked, wildcat