Old man in agony (4)

I believe the answer is:

pain

'agony' is the definition.
(thesaurus)

'old man in' is the wordplay.
'old man' becomes 'pa' (both can mean father).
'pa'+'in'='PAIN'

(Other definitions for pain that I've seen before include "Sensation of acute discomfort" , "Tiresome figure" , "can cause discomfort" , "Suffering, distress" , "French bread?" .)

I've seen this clue in The Telegraph.

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