The most common and most likely answer to this crossword clue is the 7 letter word SANDING
I've seen this crossword clue in The Daily Telegraph
S
A
N
D
I
N
G
Buddy explains!
The straight part
We know that "Polishing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case polishing = sanding.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 SANDING mean?
SANDING verb- To abrade the surface of (something) with sand or sandpaper in order to smooth or clean it.
- To cover with sand.
- To blot ink using sand.
- The act or process by which something is sanded; the application of sandpaper, etc.
- A type of dancing where the floor is covered in sand. See Sanding (dance).
- The process of testing the surface of gilding, after it has been fired, with fine sand and water.
- The process of burying oysters in sand.
- The process of applying sand to rails in railway track to aid adhesion.