The definition of certainly is absolutely or definitely.
An example of certainly used as an adverb is in the sentence, "We will certainly buy some cookies," which means "We will absolutely buy some cookies."
- beyond a doubt; surely
- Undoubtedly; definitely: This is certainly not my writing.
- By all means; of course: You may certainly join us.
- Surely: They certainly are hard workers.
(comparative more certainly, superlative most certainly)
certain + -ly