Betray a failing (6)

I believe the answer is:

defect

This clue is a double definition.

'betray' is the first definition.
(thesaurus)

'a failing' is the second definition.
(I've seen this before)

(Other definitions for defect that I've seen before include "Flaw, blemish" , "Blemish, fault" , "Flaw - change sides" , "Fault - default" , "Desert - fault" .)

I've seen this clue in The Irish Times.

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