Book seized by international court upset teacher (5)
I believe the answer is:
rabbi
'teacher' is the definition.
(I've seen this before)
'book seized by international court upset' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'seized by' is an insertion indicator.
'international court upset' becomes 'rabi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'b' placed into 'rabi' is 'RABBI'.
Can you help me to learn more?
(Other definitions for rabbi that I've seen before include "legal scholar" , "Hebrew teacher" , "Jewish minister" , "Jewish learned man" , "Religious leader in a Jewish community" .)