City between two rivers frozen (5)
I believe the answer is:
polar
'frozen' is the definition.
(thesaurus)
'city between two rivers' is the wordplay.
'two rivers' means two replacements for 'river'.
'city' becomes 'LA' (Los Angeles).
'between' means one lot of letters goes inside another.
'river' becomes 'Po' (Italian river).
'river' becomes 'r' (abbreviation for river).
'po'+'r'='por'
'la' inserted into 'por' is 'POLAR'.
(Other definitions for polar that I've seen before include "Of the cold regions" , "Relating to the highest latitudes" , "Having opposite extremes" , "Diametrically opposed -- very cold" , "Directly opposed" .)