Certain to replace the last one with the ultimate Nouveau drape (7)

I believe the answer is:

curtain

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

'drape' is the definition.
(I know that drape can be written as curtain)

I don't understand the rest of the clue.

(Other definitions for curtain that I've seen before include "Hanging material screen" , "It can be drawn" , "Window drape" , "Hanging cloth" , "Hanging, window cover" .)

I've seen this clue in the Sydney Morning Herald.

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