A command in which to succeed (5)

I believe the answer is:

order

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'a command' is the definition.
(I know that order is a type of command)

I don't understand the remainder of the clue.

(Other definitions for order that I've seen before include "American helping" , "eg OBE" , "Select from menu" , "System" , "Command or request for goods" .)

I've seen this clue in the Evening Standard.

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