Criticise lack of conservative guarantee (6)

I believe the answer is:

ensure

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'guarantee' is the definition.
(I know that guarantee can be written as ensure)

I can't explain the rest of the clue.

(Other definitions for ensure that I've seen before include "Make certain that (something occurs)" , "Make certain or safe" , "warrant" , "Guarantee" , "See run (anag)" .)

I've seen this clue in The Irish Times.

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