Covering fixed in lord's mansion from the outset (4)

I believe the answer is:

film

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

'covering' is the definition.
(I know that film is a type of wrap)

I can't explain the rest of the clue.

(Other definitions for film that I've seen before include "Skin" , "Screen" , "Thin membrane" , "Veil; cinema attraction" , "Cinema entertainment" .)

I've seen this clue in The Irish Times.

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