The most common and most likely answer to this crossword clue is the 10 letter word BORDERLINE
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More clues leading to the result BORDERLINE
Buddy explains!

The straight part
We know that "marginal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marginal = borderline.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 BORDERLINE mean?
BORDERLINE noun- A boundary or accepted division; a border.
- An individual who has borderline personality disorder.
- To border, or border on; to be physically close or conceptually akin to.
- Nearly; not clearly on one side or the other of a border or boundary, ambiguous.
- Showing bad taste.
- Exhibiting borderline personality disorder.
- Nearly; not entirely but nevertheless to a great extent