Sometimes yet can mean but or however:
-I haven't received any messages so far, yet I'm certain one is coming.
And it shows up in the idiom yet again, which, like once again, implies repeated attempts:
-I checked for messages yet again.
And finally, there's the yet that expresses an expectation of completion (the opposite of already, the expectation of incompletion):
-Are we there yet?
-Are you done yet?
Yes. We're there and we're done.
- For Teachers