Boredom oddly not seen in Lennon's music (5)
I believe the answer is:
ennui
'boredom' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ennui that I've seen before include "Feeling of dissatisfaction" , "to make one list less when connected" , "The feeling of being bored" , "Boredom or discontent" , "What's tedious and instils such listlessness" .)