KH: Haha, sure... wait, how do you say that in English?
Me: Um... you know... "sit in on a class..."
KH: Isn't there a specific word for it?
Me: Yeah, there is... it's at the tip of my tongue...
Me: I'm losing my English!
Me: Give me one second.
KH: Your second's up!
Me: Wait, I swear I know this!
***frantically IMs Dave/Oliver in Boston***
Me: I got it! It's called "AUDITING!"
청강하다 = to audit a course/sit in on a lecture