Something fishy in South American greeting (5)
I believe the answer is:
sushi
'something fishy' is the definition.
(dish which often includes fish)
'south american greeting' is the wordplay.
'south' becomes 'S' (synonyms).
'american' becomes 'us' (abbreviation for United States).
'greeting' becomes 'hi' (hi is a kind of greeting).
's'+'us'+'hi'='SUSHI'
'in' is the link.
(Other definitions for sushi that I've seen before include "Rice and raw fish wrapped in seaweed" , "Rice, seafood cuisine" , "Japanese rice-based dish" , "oriental dish" , "Food from Japan" .)