Discovered Ypres Command is secure in advance (8)

I believe the answer is:

preorder

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'secure in advance' is the definition.
The definition suggests a singular noun which matches the answer.

'discovered ypres command' is the wordplay.
'discovered' says to take the centre (dis-covered - outer letters removed).
'command' becomes 'order' (order is a kind of command).
The middle of 'ypres' is 'pre'.
'pre'+'order'='PREORDER'

'is' acts as a link.

Can you help me to learn more?

(Another definition for preorder that I've seen is " Reserve (something) before it's available".)

I've seen this clue in The Telegraph.

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