South American greeting snack food (5)
I believe the answer is:
sushi
'snack food' is the definition.
(type of Japanese food)
'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'
(Other definitions for sushi that I've seen before include "rice dishes" , "fare from Japan" , "'Dish of rice, vegetables and raw fish (5)'" , "Raw fish dishes" , "Japanese rice-based dish" .)