Use the adverb surely to emphasize your certainty about a point. For example, you could tell your friend that her painting is so good that she'll surely win the art contest.
The word surely can fill in for definitely or absolutely. It comes in handy especially when you're surprised that anyone would doubt what you're saying: "I can't believe the school banned that book. Surely kids should have access to classic literature." Surely comes from the same roots as sure, from the Old French seur, "secure, undoubted, or dependable," and the Latin securus, "free from care, untroubled, or safe."