Monotony (15)
'monotony' is the definition.
(thesaurus)
This is all the clue.
'monotony' is the definition.
(monotony can mean dullness or tedium)
This is all the clue.
(Other definitions for tedium that I've seen before include "Banality" , "Dullness, monotony" , "boring" , "Boredom with monotony" , "Boredom or dullness" .)