Van is seen moving with simplicity (9)

I believe the answer is:

naiveness

'simplicity' is the definition.
(thesaurus)

'van is seen moving' is the wordplay.
'moving' indicates an anagram.
'van'+'is'+'seen'='vanisseen'
'vanisseen' is an anagram of 'NAIVENESS'.

'with' acts as a link.

I've seen this clue in The Everyman puzzle in The Observer.

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