At a wake, stand and drink to an auditor (4)

I believe the answer is:

bier

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'at' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

I can't explain the rest of the clue.

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(Other definitions for bier that I've seen before include "Platform for coffin" , "Brie (anag.)" , "Og high standing" , "Movable stand for coffin" , "Litter" .)

I've seen this clue in The Sunday Times.

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