A deficiency, I'm sorry to say (5)

I believe the answer is:

alack

'i'm sorry to say' is the definition.
(I've seen this before)

'a deficiency' is the wordplay.
'deficiency' becomes 'lack' (synonyms).
'a'+'lack'='ALACK'

(Other definitions for alack that I've seen before include "Old expression of dismay" , "expression of regret" , "I mourn" , "Alas (archaic)" , "I'm sorry to say" .)

I've seen this clue in the Evening Standard.

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