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Big
noise
as
good
egg
splits
log
(9)
Big noise as good egg splits log (9)
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The definition is at the beginning of the clue.
How the clue works
The definition is Big noise — someone important and influential. For the wordplay, take G (good) and NIT (a louse's egg) and slot them inside DIARY (a log), splitting it as DI then GNIT then ARY.