For a certainty :
For sure :
Most certainly :
Most probably :
Of a surety :
It must be the case that, Certainly, Firmly, For certain
English Meaning :
(Adverb : Definitely or positively (`sure' is sometimes used informally for `surely')
Example : She walked firmly and surely , every footstep getting stronger, and went to the door.
Word Example from TV Shows :
But SURELY a future Nobel Prize winner
can figure it out.
(The Big Bang Theory Season 4, Episode 18)
With certainty :