Hunter ahead outside city (5)
I believe the answer is:
orion
'hunter' is the definition.
(constellation)
'ahead outside city' is the wordplay.
'ahead' becomes 'on' (synonyms).
'outside' indicates putting letters inside.
'city' becomes 'rio' (Rio de Janeiro).
'on' placed around 'rio' is 'ORION'.
(Other definitions for orion that I've seen before include "Belted constellation" , "Constellation on the celestial equator -- giant hunter of Greek mythology" , "Hunter slain by Artemis" , "One who would hunt" , "Constellation in the form of a belt" .)