I'm entertained in a form that's 'nouvelle vague' (13)

I believe the answer is:

indeterminate

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

'vague' is the definition.
(I've seen this before)

'i'm entertained in a form that's nouvelle' is the wordplay.
'i'm entertained' can be anagrammed to 'INDETERMINATE'.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for indeterminate that I've seen before include "Unfixed, uncertain" , "Not exactly known" , "Having no fixed value" , "uncertain result?" , "Not precisely fixed" .)

I've seen this clue in The Telegraph.

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