The Collaborative International Dictionary of English v.0.48:

Unadventurous \Unadventurous\
   See adventurous.

WordNet (r) 3.0 (2006):

unadventurous
    adj 1: lacking in boldness [ant: adventuresome, adventurous]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "unadventurous":
   canny, careful, cautious, circumspect, deliberate, discreet,
   gingerly, guarded, heedful, hesitant, judicious,
   leaving out nothing, mindful, noncommittal, on guard,
   overlooking no possibility, pawky, politic, prudent, regardful,
   safe, slow to act, tentative, thorough, uncommunicative, undaring,
   unenterprising, unprecipitate