Really worried, having lost pound in advance (5)

I believe the answer is:

early

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'in advance' is the definition.
('early' can be similar in meaning to 'in advance')

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

Can you help me to learn more?

(Other definitions for early that I've seen before include "sooner than expected" , "Prematurely" , "Premature" , "before anyone else?" , "Before the expected time" .)

I've seen this clue in The Mirror.

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