Something stimulating to do up (3)

I believe the answer is:

pep

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'do up' is the definition.
Although both the answer and definition are singular nouns, I cannot 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 pep that I've seen before include "Vim and vitality" , "Go" , "Energy, liveliness" , "Energy, zip" , "Palindrome for vitality or energy" .)

I've seen this clue in the Evening Standard.

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