Urge of significant duration in capital of Greece (7)
I believe the answer is:
longing
'urge' is the definition.
(thesaurus)
'of significant duration in capital of greece' is the wordplay.
'of significant duration' becomes 'long'.
'capital of' indicates taking the first letters.
The initial letter of 'greece' is 'g'.
'long'+'in'+'g'='LONGING'
(Other definitions for longing that I've seen before include "Deeply felt desire" , "Yearning desire" , "Earnest, heartfelt desire" , "Hunger" , "thirsty" .)