Crossword Genius

Base missing from stone grate (3)

Ross

I believe the answer is:

rub

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'grate' is the definition.
(I know that grate is a more specific form of the action rub)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for rub that I've seen before include "Ointment for skin" , "Abrade" , "Ay, there's the - (Hamlet)" , "Ointment; chief difficulty" , "Central difficulty" .)

I've seen this clue in The Times.
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