Uncertain moment with Juliet disappearing (4)

I believe the answer is:

iffy

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'uncertain' is the definition.
('iffy' can be similar in meaning to 'uncertain')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for iffy that I've seen before include "Informally dubious or uncertain" , "Chancy, suspect" , "Doubtful (colloq.)" , "Problematic" , "Colloquially uncertain or doubtful" .)

I've seen this clue in The Telegraph.

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