Frequency: The word is one of the 3000 most common words in English.
1.
You use surely to emphasize that you think something should be true, and you would be surprised if it was not true.
You're an intelligent woman, surely you realize by now that I'm helping you...
If I can accept this situation, surely you can.
ADV: ADV with cl/group [emphasis]
2.
If something will surely happen or is surely the case, it will definitely happen or is definitely the case. (FORMAL)
He knew that under the surgeon's knife he would surely die...
He is an artist, just as surely as Rembrandt or any other first-rate portrait painter is one.
= certainly
ADV: ADV with cl, ADV before v
3.
If you say that something is happening slowly but surely, you mean that it is happening gradually but it is definitely happening.
Slowly but surely she started to fall in love with him...
PHRASE: PHR with cl