Call a duke in Brazilian city (5)
I believe the answer is:
radio
'call' is the definition.
(I've seen this in another clue)
'a duke in brazilian city' is the wordplay.
'duke' becomes 'd' (abbreviation).
'in' indicates putting letters inside.
'brazilian city' becomes 'Rio' (Rio de Janeiro).
'a'+'d'='ad'
'ad' put inside 'rio' is 'RADIO'.
(Other definitions for radio that I've seen before include "listening device" , "MW, LW or FM sound source" , "Communications device" , "broadcasting station" , "Contact" .)