Unusually impressive, allowing freedom of behaviour (10)

I believe the answer is:

permissive

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

'allowing freedom of behaviour' is the definition.
'permissive' can be an answer for 'allowing' (thesaurus). I'm not certain of the 'freedom of behaviour' bit.

'unusually impressive' is the wordplay.
'unusually' indicates an anagram.
'impressive' anagrammed gives 'PERMISSIVE'.

Can you help me to learn more?

(Other definitions for permissive that I've seen before include "Free" , "Showing indulgence" , "Lenient, indulgent" , "Liberal, broad-minded" , "Like our society" .)

I've seen this clue in The Telegraph.

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