Regret Old Testament book half missing (6)

I believe the answer is:

lament

'regret' is the definition.
(synonyms)

'old testament book half missing' is the wordplay.
'old testament book' becomes 'Lamentations' (Lamentations is a book of the Old Testament).
'half missing' suggests halving the letters.
'lamentations' halved is 'LAMENT'.

(Other definitions for lament that I've seen before include "Show of sorrow" , "Sad song" , "Cry of sorrow" , "Mourn in mental way (6)" , "complaint" .)

I've seen this clue in The Times.

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