A chance to pass on what you’ve learned (4)
I believe the answer is:
exam
'a chance' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for exam that I've seen before include "Important test" , "School test (colloq.)" , "Something to sit" , "End-of-course assessment" , "'Test, in short (4)'" .)