His victory in the election is 'almost a certainty'. [=it is nearly certain/definite that he will win the election]
It is difficult to say 'with certainty' [=in a certain or definite way] which of the plays was written first.
Scientists still do not know with any degree of 'certainty' why the disease spread so quickly.
(..) Michael, that's highly distressing! Lawrence.... That is not all of our liquidity! And I'm not certain that you really understand this trade. This is a certainty. Mike, i consider myself a mentor to you. But our company is not comfortable with this investment. Am i being clear? - Lawrence (..)2015 The Big Short