Atmosphere around capital city cold and extremely tense (7)
I believe the answer is:
climate
'atmosphere' is the definition.
(thesaurus)
'around capital city cold and extremely tense' is the wordplay.
'around' indicates putting letters inside.
'capital city' becomes 'lima' (I've seen this before**).
'cold' becomes 'c' (eg on taps).
'and' means one lot of letters go next to another.
'extremely' means to remove the middle letters.
'tense' with its centre removed is 'te'.
'c'+'te'='cte'
'lima' placed inside 'cte' is 'CLIMATE'.
(Other definitions for climate that I've seen before include "Weather etc" , "Atmospheric conditions" , "General weather conditions in an area" , "Atmosphere" , "Mail, etc (anag.)" .)