Noun
an unpredictable phenomenon
Source: WordNetit's a toss-up whether he will win or lose Source: Internet
Marder p. 169 The system of testing shells, which remained in use up to 1944, meant that, statistically, a batch of shells of which 70% were faulty stood an even chance of being accepted. Source: Internet
This gives the partnership a better than even chance of success in making the contract, whereas without a response (and without Stayman), the contract would likely be set. Source: Internet