Meaning of “certainly” - Learner’s Dictionary

certainly

adverb uk us /ˈsɜːtənli/
WITHOUT DOUBT

A2 used to emphasize something and show that there is no doubt about it:

Their team certainly deserved to win.
"Are your parents paying for dinner?" "I certainly hope so."
She may never find out. I'm certainly not going to tell her.
"Do you regret what you said?" "Certainly not!"
OF COURSE

A2 used to agree to a request:

"Could you pass the salt, please?" "Certainly."

(Definition of “certainly” from the Cambridge Learner’s Dictionary © Cambridge University Press)