The most common and most likely answer to this crossword clue is the 8 letter word POPSICLE
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More clues leading to the result POPSICLE
Buddy explains!

The straight part
We know that "American sucker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case american sucker = popsicle.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 POPSICLE mean?
POPSICLE noun- Frozen fruit juice, flavored sugar water or the like, on a stick, of a size to be one serving.
- Something cold or frozen.