Undoubtedly; certainly: You surely can't be serious. (adverb)
Without fail: Slowly but surely spring returns. (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 "surely" in a sentence
"There was a wife and a little, little baby, "Oh, _so_ little!" far up on the mountain-side; they would starve; surely, _surely_ they would starve!"
""Oh, surely, _surely_ now, some ship will sight it and come in!" proclaimed Jean, as she turned to scan the sea, her face alight with the faith inspired by the faded colors."
"But to him the title surely belongs; and there is no competent judge, who, when made aware of the great talents and acquisitions, theoretical and practical, of Mr. Lewis in the science of music, will not cheerfully accord it to him."