Lack of development in deer country (10)
I believe the answer is:
stagnation
'lack of development' is the definition.
'stagnation' can be an answer for 'lack' (I have seen 'Lack of activity ' mean 'stagnation' so perhaps 'lack' could also mean 'stagnation'). I'm not sure about the 'of development' bit.
'deer country' is the wordplay.
'deer' becomes 'stag' (stag is a kind of deer).
'country' becomes 'nation' (synonyms).
'stag'+'nation'='STAGNATION'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for stagnation that I've seen before include "Nothing much happens" , "Inactivity" , "Failure to develop" , "sluggish" , "It's still" .)