Guy terribly green, syringe nurse is holding? (6)

I believe the answer is:

ingenu

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'guy terribly' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'green syringe nurse is holding?' is the wordplay.
'is holding?' indicates the answer is hidden within the clue.
'INGENU' is hidden within 'green syringe nurse'.

Can you help me to learn more?

(Another definition for ingenu that I've seen is " Green Man".)

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