Other forms: probabilities
Probability is how likely something is to happen. The thirty per cent chance of rain on your phone, the odds of a coin landing heads, the chance that this bus is late again.
Probability is also the branch of maths that measures this, the one taught with dice, cards and coloured balls in a bag; there a probability is a number between 0 and 1, where 0 never happens and 1 always does. It takes OF before a noun and THAT before a clause: the probability of rain, a high probability that the flight is cancelled. It can be counted or uncounted — probabilities plural is normal in maths, singular in ordinary talk. The fixed phrase in all probability means almost certainly. The family around it is probable, probably and improbable.
1nounlogicHow likely it is that something will happen or is true.
“The probability of a white Christmas here is very low.”
2nounprobabilityThe branch of mathematics that measures how likely events are.
“We spent a term on probability and statistics.”
3nounnumberA number between 0 and 1 expressing how likely an event is.
“Each face of a fair die has a probability of one sixth.”
Too few real examples of this word to estimate which sense is commonest.
Probability came through Middle French probabilité from Latin probābilitās, glossed "probability, credibility", built on probābilis, "probable, credible". The Latin was about how believable a claim was, not about numbers. The arithmetic arrived long afterwards, and the older sense still shows in the phrase in all probability.
Latin
probābilitās — probability, credibility
Middle French
probabilité
English, today
probability
Built from
From Middle French probabilité, from Latin probābilitās (“probability, credibility”), from probābilis (“probable, credible”).
Etymology from Wiktionary, CC BY-SA