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Carved from tufa stone, immoveable (4)

Ross

I believe the answer is:

fast

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'immoveable' is the definition.
(synonyms)

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(Other definitions for fast that I've seen before include "Don't scoff" , "Rapid - diet" , "Quick - abstain from food" , "Secure; speedy" , "Starve; quick" .)

I've seen this clue in The Guardian.
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