overchance adjective 1noun 1forms 3 adjective1 •Occurring more than expected by mere chance or probability.It was claimed that an overchance number of correct answers was scored. — 1969 noun1 •A likelihood that is greater than when all options are equally probable.At the second birth there is still an overchance in favor of a boy. — 1906 formsoverchances · more overchance · most overchance