Extended picnic? (6,3)

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6,3

spread out

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'extended picnic?' is the definition.
'spread out' can be an answer for 'extended' (thesaurus). I am not certain of the 'picnic?' bit.

'extended picnic?' is the wordplay.
'extended' becomes 'spread' (synonyms).
'picnic?' becomes 'out' (I can't explain this - if you can you should give a lot more credence to this answer).
'spread'+'out'='SPREAD OUT'

Can you help me to learn more?

(Other definitions for spread out that I've seen before include "Move so as to cover a wider area" , "move apart" .)

I've seen this clue in The Guardian.

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