Hidden from view, French number seven, not five (6)

I believe the answer is:

unseen

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'hidden from view' is the definition.
(I've seen this before)

'french number seven not five' is the wordplay.
'french number' becomes 'un' (I can't justify this - if you can you should believe this answer much more).
'not' is a deletion indicator.
'five' becomes 'V' (Roman numeral).
'seven' with 'v' taken out is 'seen'.
'un'+'seen'='UNSEEN'

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(Other definitions for unseen that I've seen before include "Unnoticed" , "not exercising pupils?" , "Hidden from view" , "Translation exercise" , "Not perceived or observed" .)

I've seen this clue in The Times.

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