Vivacity seen in Brazilian capital and port (4)
I believe the answer is:
brio
'vivacity' is the definition.
(thesaurus)
'brazilian capital and port' is the wordplay.
'capital' says to take the initial letters.
'and' is a charade indicator (letters next to each other).
'port' becomes 'rio' (I've seen this before).
The initial letter of 'brazilian' is 'b'.
'b'+'rio'='BRIO'
'seen in' acts as a link.
(Other definitions for brio that I've seen before include "Spiritedness" , "Animation (Italian)" , "Drive" , "'Con ..., musically with vigour (4)'" , "Vigour, vivacity" .)