Leaves trip well-centred at zero altitude (3-5)

I believe the answer is:

sea-level

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'zero altitude' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?

'leaves trip well-centred' is the wordplay.
'trip' indicates an anagram.
'centred' says to take the centre.
The middle letters of 'well' are 'el'.
'leaves' anagrammed gives 'sealev'.
'sealev'+'el'='SEA-LEVEL'

'at' acts as a link.

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I've seen this clue in the Sydney Morning Herald.

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