Tool reportedly used to underpin ginormous bone (7)

I believe the answer is:

ossicle

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'bone' is the definition.
(ossicle is a kind of bone)

I don't understand how the remainder of the clue works.

(Other definitions for ossicle that I've seen before include "Small bone, especially one in the middle ear" , "Very small bone, in the middle ear say" , "A hammer" .)

I've seen this clue in The Independent.

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