The most common and most likely answer to this crossword clue is the 6 plus 5 letter word BUENOS AIRES
B
U
E
N
O
S
A
I
R
E
S
Buddy explains!
The straight part
We know that "S American city" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case s american city = buenos aires.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.