Crossword Genius

Problem of pain (8)

Ross

I believe the answer is:

headache

I believe this clue is a double definition.

'problem' is the first definition.
(headache can mean a problem or annoyance)

'pain' is the second definition.
(headache is a kind of pain)

'of' is the link.

(Other definitions for headache that I've seen before include "Problem, nuisance" , "Informally a worrying problem - take an asprin" , "Cause of worry/trouble" , "trial" , "nasty problem" .)

I've seen this clue in The Globe and Mail.
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