Round capital city, cold and extremely tense atmosphere (7)
I believe the answer is:
climate
'atmosphere' is the definition.
(I've seen this in another clue)
'round capital city cold and extremely tense' is the wordplay.
'round' indicates putting letters inside.
'capital city' becomes 'lima' (capital of Peru).
'cold' becomes 'c' (eg on taps).
'and' is a charade indicator (letters next to each other).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'tense' with its centre taken out is 'te'.
'c'+'te'='cte'
'lima' placed inside 'cte' is 'CLIMATE'.
(Other definitions for climate that I've seen before include "The regular weather conditions of a region" , "Prevailing trend" , "National weather conditions" , "Prevailing weather conditions" , "Prevailing public attitude" .)