Frequency: The word is one of the 1500 most common words in English.
1.
You use ~ to indicate that you are not sure whether something is true or might happen.
Exercise will not only lower blood pressure but ~ protect against heart attacks...
They were smartly but casually dressed; ~ students...
Do you think that he could ~ be right?
ADV: ADV with cl/group, ADV with v vagueness
2.
You use ~ to emphasize that you are surprised, puzzled, or shocked by something that you have seen or heard.
It was the most unexpected piece of news one could ~ imagine...
ADV: ADV before v emphasis
3.
You use ~ to emphasize that someone has tried their hardest to do something, or has done it as well as they can.
They’ve done everything they can ~ think of...
ADV: ADV before v emphasis
4.
You use ~ to emphasize that something definitely cannot happen or definitely cannot be done.
No I really can’t ~ answer that!
ADV: with brd-neg, ADV before v emphasis