I'm powerful but helpless (8)

I believe the answer is:

impotent

'helpless' is the definition.
(I've seen this in another clue)

'i'm powerful' is the wordplay.
'powerful' becomes 'potent' (similar in meaning).
'im'+'potent'='IMPOTENT'

'but' is the link.

(Other definitions for impotent that I've seen before include "Useless" , "Mon petit may be powerless" , "Ineffective" , "Powerless like mon petit" , "Helpless, powerless" .)

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

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