Nothing's unacceptable to break my boredom (8)
I believe the answer is:
monotony
'boredom' is the definition.
(thesaurus)
'nothing's unacceptable to break my' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'unacceptable' becomes 'noton' (I've seen this before).
'to break' indicates putting letters inside.
'o'+'noton'='onoton'
'onoton' inserted within 'my' is 'MONOTONY'.
(Other definitions for monotony that I've seen before include "Unvarying tedium" , "Lack of excitement" , "It's wearisome" , "fixed routine" , "Sameness" .)