Happening still to Turkish capital (5)
I believe the answer is:
event
'happening' is the definition.
(I've seen this in other clues)
'still to turkish capital' is the wordplay.
'still' becomes 'even' (synonyms).
'to' is a charade indicator (letters next to each other).
'capital' suggests taking the first letters.
The initial letter of 'turkish' is 't'.
'even'+'t'='EVENT'
(Other definitions for event that I've seen before include "High jump, say" , "Particular happening" , "Incident, occurrence" , "important" , "special occasion" .)