Shifting angularities — it’s a pain (9)

I believe the answer is:

neuralgia

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'pain' is the definition.
(neuralgia is a kind of pain)

I can't explain the remainder of the clue.

(Other definitions for neuralgia that I've seen before include "Sharp pain extending along nerves" , "Acute pain of the nerves" , "Source of pain" , "Pain from damaged nerve" , "sort of pain" .)

I've seen this clue in The Hindu.

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