Improvised setter's cue on origin of universe (9)

I believe the answer is:

impromptu

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

'setter's cue on origin of universe' is the wordplay.
'setter's' becomes 'I'm' (referring to the crossword setter).
'cue on' becomes 'prompt' (prompt is a kind of cue. I am not sure about the 'on' bit.).
'origin of' suggests taking the first letters.
The first letter of 'universe' is 'u'.
'im'+'prompt'+'u'='IMPROMPTU'

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(Other definitions for impromptu that I've seen before include "Piano piece" , "Spontaneous" , "unrehearsed piece" , "Unplanned; composition" , "Unprepared" .)

I've seen this clue in The Telegraph.

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