Barbara Windsor? (6)

I believe the answer is:

castle

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'barbara windsor?' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

This is the entire clue.

Can you help me to learn more?

(Other definitions for castle that I've seen before include "Rook, on chess board" , "Move king to safety - stronghold" , "Stronghold - chessman" , "Chateau" , "Make chess move involving king and rook" .)

I've seen this clue in The Irish Independent.

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