'probability' refer to 'greater possibility', but how to denote a generic word that mean 'less possibility' in English?
There is difficulty because "probability" has a technical meaning, that doesn't quite match the adjective "probable".
It would be correct to say that the probability is 0.001%. But you wouldn't say that such an event was probable. On the other hand you don't give numeric values to "possibilities". An example may illustrate this:
Moldova plays Spain at football. There are three possibilities: Moldova can win, lose or draw. The probability of a win is very low, less than 1%.
If you want a noun you could use "a chance": "There is a chance that Moldova will win". The phrase "outside chance" is more explicitly low in probability.
If you can use an adjective, things are easier, since the adjective "probable" does imply more likely than "possible".
The BBC recommends this list for students of maths.
certain > very likely > likely > evens > unlikely > very unlikely > impossible.
"Likely" is synonymous with "probable". Possible, but not probable, covers the range from "evens" to very unlikely.
You could use "very unlikely" to describe an event such as "It is very unlikely that Moldova will beat Spain."