Penny quit cutting corners in boredom (5)
I believe the answer is:
ennui
'boredom' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ennui that I've seen before include "Effect of boredom" , "Boredom or discontent" , "tiredness" , "Boredom in France" , "depression" .)