Undoubtedly; definitely: This is certainly not my writing. (adverb)
By all means; of course: You may certainly join us. (adverb)
Surely: They certainly are hard workers. (adverb)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "certainly" in a sentence
"The R rating should certainly mean there is a lot more to follow that they can't show us in the trailer..certainly should make it a lot edgier."
"The scientific issues were what initially brought me to this debate, but the religious implications are certainly right there in your face as well...and, both subjects are *certainly* interesting."
"You are certainly quite right about it, Porfiry began gaily, looking with extraordinary simplicity at Raskolnikov (which startled him and instantly put him on his guard) certainly quite right in laughing so wittily at our legal forms, he-he!"