The most common and most likely answer to this crossword clue is the 7 letter word *SATIN*
I've seen this crossword clue in The Guardian
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Buddy explains!

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 *SATIN* mean?
*SATIN* noun- A cloth woven from silk, nylon or polyester with a glossy surface and a dull back. (The same weaving technique applied to cotton produces cloth termed sateen).
- To make (paper, silver, etc.) smooth and glossy like satin.
- Semigloss.