Crossword Genius

Timid hangman’s developed powerful strength (5,3,4)

Ross

I believe the answer is:

might and main

'powerful strength' is the definition.
('might and main' is a term for one's strength)

'timid hangman's developed' is the wordplay.
'developed' indicates an anagram.
'timid'+'hangman'='timidhangman'
'timidhangman' is an anagram of 'MIGHT AND MAIN'.

I've seen this clue in The Times.
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