Earnest South American touring eastern port (7)
I believe the answer is:
serious
'earnest' is the definition.
('serious' can be similar in meaning to 'earnest')
'south american touring eastern port' is the wordplay.
'south american' becomes 'sus' (I've seen this in other clues).
'touring' is an insertion indicator (touring can mean going round).
'eastern' becomes 'e'.
'port' becomes 'rio' (I've seen this before).
'e'+'rio'='erio'
'sus' enclosing 'erio' is 'SERIOUS'.
(Other definitions for serious that I've seen before include "Earnest - important" , "Important -- grave" , "Solemn, thoughtful" , "Stern" , "Earnest; vital" .)