Boredom of nun going mad in eastern island (5)
I believe the answer is:
ennui
'boredom' is the definition.
(I know that boredom can be written as ennui)
'nun going mad in eastern island' is the wordplay.
'going mad' indicates an anagram.
'in' indicates putting letters inside.
'eastern' shows that the letters should be reversed in order (letters written right to left or east to west).
'island' becomes 'ie' (I am not sure about this - if you are sure you should believe this answer much more).
'ie' backwards is 'ei'.
'nun' anagrammed gives 'nnu'.
'nnu' going within 'ei' is 'ENNUI'.
'of' is the link.
Can you help me to learn more?
(Other definitions for ennui that I've seen before include "Boredom, languor" , "The feeling of being bored" , "French boredom and lassitude" , "to make one list less when connected" , "Listless boredom" .)