The most common and most likely answer to this crossword clue is the 10 letter word GRINDSTONE
I've seen this crossword clue in The Times
G
R
I
N
D
S
T
O
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E
Buddy explains!
The straight part
We know that "something to add polish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something to add polish = grindstone.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 GRINDSTONE mean?
GRINDSTONE noun- An abrasive wheel for sharpening, polishing or grinding.