Informal address given by pioneer of bacteriology to an audience (4)

I believe the answer is:

cock

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'audience' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

I cannot understand how the rest of the clue works.

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(Other definitions for cock that I've seen before include "Component of gun" , "Adult male bird" , "Get ready to shoot" , "Pull back a gun's hammer in readiness to shoot" , "sunshine" .)

I've seen this clue in The Guardian.

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