Nothing unacceptable in my dull routine (8)
I believe the answer is:
monotony
'dull routine' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'nothing unacceptable in my' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'unacceptable' becomes 'not on' (something 'not on' is unacceptable or frowned upon).
'in' means one lot of letters goes inside another.
'o'+'noton'='onoton'
'onoton' put within 'my' is 'MONOTONY'.
Can you help me to learn more?
(Other definitions for monotony that I've seen before include "It's wearisome" , "Tedious lack of variety" , "Unvarying tedium" , "Lack of excitement" , "Tediousness" .)