Wearisomeness (6)
I believe the answer is:
tedium
'wearisomeness' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tedium that I've seen before include "Boredom, tiresomeness" , "Dullness, monotony" , "Boredom, mental weariness" , "State of being bored" , "Banality" .)