Learner's definition of CERTAINLY
1 : without doubt : definitely
— sometimes used for emphasis
It will certainly rain tomorrow.
This year's festival was certainly much better than last year's.
Certainly [=surely] you can do a better job than that!
I'm certainly going to try.
The new version is most certainly easier to use.
The snake that bit her was almost certainly poisonous.
He didn't get the raise he was hoping for, but he's certainly not complaining.
I certainly didn't mean to offend anyone.
2 : of course — used to answer questions
“Can I speak to you for a moment?” “Certainly.”
“Did I offend you?” “Oh, certainly not.” [=no, you did not offend me at all]
“May I join you?” “You most certainly may.”