Nearly give birth to a cow in a rocky hollow (4)

I believe the answer is:

cave

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'hollow' is the definition.
(caving is a kind of hollowing)

I cannot understand how the rest of the clue works.

(Other definitions for cave that I've seen before include "hole" , "Watch out" , "Natural hollow in side of hill or cliff" , "Natural underground chamber" , "Natural underground space" .)

I've seen this clue in the Sydney Morning Herald.

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