Agitated nun that is upset by life's tedium (5)
I believe the answer is:
ennui
'tedium' is the definition.
(I know that tedium can be written as ennui)
'agitated nun that is upset by life's' is the wordplay.
I cannot really see how this works, but
an anagram of 'nun' is 'nnu' which is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ennui that I've seen before include "Weary feeling" , "Effect of boredom" , "Mental weariness" , "Boredom, dullness" , "doldrums" .)