Dubious where first item taken from second (4)

I believe the answer is:

iffy

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'dubious' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for iffy that I've seen before include "Dubious (colloq.)" , "Doubtful (colloq.)" , "Dubious, risky (inf.)" , "Chancy, suspect" , "Uncertain (colloq.)" .)

I've seen this clue in The Times.

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