Dullness of deer country (10)
I believe the answer is:
stagnation
'dullness' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'deer country' is the wordplay.
'deer' becomes 'stag' (stag is a kind of deer).
'country' becomes 'nation' (synonyms).
'stag'+'nation'='STAGNATION'
'of' is the link.
Can you help me to learn more?
(Other definitions for stagnation that I've seen before include "standstill" , "Process of reducing activity" , "It's still" , "Lack of movement or growth" , "State of little activity" .)