The most common and most likely answer to this crossword clue is the 7 letter word BURNISH
B
U
R
N
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S
H
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The straight part
We know that "sheen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sheen = burnish.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 BURNISH mean?
BURNISH noun- Polish; lustre.
- To make smooth or shiny by rubbing; to polish; to shine.
- To shine forth; to brighten; to become smooth and glossy, as from swelling or filling out; hence, to grow large.
- (metaphoric) To make appear positive and highly respected.