Exam's ultimate test, right? (5)
I believe the answer is:
moral
'right?' is the definition.
(similar in meaning)
'exam's ultimate test' is the wordplay.
'ultimate' indicates one should take the final letters.
'test' becomes 'oral' (oral is a type of examination).
The final letter of 'exam' is 'm'.
'm'+'oral'='MORAL'
(Other definitions for moral that I've seen before include "ethical standard" , "Lesson offered by story" , "ethical principle" , "knowing right from wrong" , "Honourable" .)