The most common and most likely answer to this crossword clue is the 6 letter word CHINOS
I've seen this crossword clue in Financial Times
C
H
I
N
O
S
More clues leading to the result CHINOS
Buddy explains!

The straight part
We know that "American pants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case american pants = chinos.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.
What does CHINOS mean?
CHINOS noun- Trousers made from chino