1 : occurring or appearing or singled out by chance; "seek help from casual passers-by"; "a casual meeting"; "a chance occurrence"
1 : be the case by chance
1 : a measure of how likely it is that some event will occur; a number expressing the ratio of favorable cases to the whole number of cases possible; "the probability that an unbiased coin will fall with the head up is 0.5"; "if that phone call is for me, chances are it's my wife"
2 : the possibility of future success
3 : a possibility due to a favorable combination of circumstances