Meaning : 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.
Example :
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.
Synonyms : chance
Meaning : The quality of being probable. A probable event or the most probable event.
Example :
For a while mutiny seemed a probability.
Going by past experience there was a high probability that the visitors were lost.
The quality of being improbable.
Impossibility should never be confused with improbability.