Express at even greater length? (6)

I believe the answer is:

expand

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'express' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for expand that I've seen before include "Amplify" , "Become larger or more extensive" , "Dilate" , "Fill out" , "Branch out" .)

I've seen this clue in The Globe and Mail.

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