I'm going back out — get Brian under way at the centre (5)

I believe the answer is:

adieu

I'm a little stuck... Click here to teach me more about this clue!

'i'm going' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for adieu that I've seen before include "farewell message" , "Goodbye in France" , "Goodbye to the French" , "Goodbye, monsieur" , "the last word in Paris" .)

I've seen this clue in The Guardian.

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