WordNet sense 1 (a source of danger; a possibility of incurring loss or misfortune):

endangerment, jeopardy, peril, risk

WordNet sense 2 (an unknown and unpredictable phenomenon that causes an event to result one way rather than another):

chance, fortune, luck

WordNet sense 3 (put at risk):

adventure, jeopardize, stake, venture

WordNet sense 4 (take a risk in the hope of a favorable outcome):

gamble, run a risk, take a chance, take chances

WordNet sense 5 (put forward, of a guess, in spite of possible refutation):

guess, pretend