One leaving someone on standby to search endlessly for battlefield? (8)

I believe the answer is:

waterloo

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But I can't explain it at all! Could you help me understand?

(Other definitions for waterloo that I've seen before include "London rail terminus" , "Historical action" , "Lose a decisive contest - meet your . . . . . . . . as Napoleon did" , "Heavy defeat" , "battle in Belgium" .)

I've seen this clue in The Times.

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