certainly

Etymology

From Middle English certeynly; equivalent to certain + -ly.

adv

1. In a way which is certain; with certainty.
   he verily thought he had young live frogs in his belly, qui vivebant ex alimento suo, that lived by his nourishment, and was so certainly persuaded of it, that for many years following he could not be rectified in his conceit. , I.iii.2.2
   The torque was "built up" in the special back axle and the car crawled tankwise but very certainly over the obstacles without a jar or hesitation. 1923, A. A. Hill, Automobile Dealer and Repairer, page 30
2. Without doubt, surely.
   The accident was certainly caused by human error.
   That was certainly sweet of him.
   You may certainly join us for dinner.
   WikiLeaks did not cause these uprisings but it certainly informed them. The dispatches revealed details of corruption and kleptocracy that many Tunisians suspected, but could not prove, and would cite as they took to the streets. 2013-06-07, Gary Younge, “Hypocrisy lies at heart of Manning prosecution”, in The Guardian Weekly, volume 188, number 26, page 18
3. An emphatic affirmative answer; of course.
   Would you like it with ice?  Certainly, and with lemon please.