Hidden city shelter (6)
I believe the answer is:
latent
'hidden' is the definition.
(thesaurus)
'city shelter' is the wordplay.
'city' becomes 'la' (Los Angeles).
'shelter' becomes 'tent' (tent is a kind of shelter**).
'la'+'tent'='LATENT'
(Other definitions for latent that I've seen before include "Existing but not yet manifest" , "Unrealised, potential" , "'Hidden, undeveloped (6)'" , "Inactive - potential" , "Potentially existing but not presently evident" .)