Voluntary worker using only a pencil? (8)

I believe the answer is:

freehand

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'only a pencil?' is the definition.
I can't tell whether this definition defines the answer.

'voluntary worker' is the wordplay.
'voluntary' becomes 'free' (similar in meaning).
'worker' becomes 'hand' (hand is a kind of worker).
'free'+'hand'='FREEHAND'

'using' acts as a link.

Can you help me to learn more?

(Other definitions for freehand that I've seen before include "drawn in the normal way" , "Style of drawing - carte blanche" , "given to plenipotentiary" , "Ignoring ruler, perhaps" , "Without drawing aids" .)

I've seen this clue in The Independent.

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