Shutter usually closed at night (6)

I believe the answer is:

eyelid

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

'shutter' is the definition.
(I have seen 'Facial shutter' mean 'eyelid' so perhaps 'shutter' could also mean 'eyelid')

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for eyelid that I've seen before include "The blinking thing!" , "Facial shutter" , "Natural optic covering" , "Ocular closer" , "Optic membrane" .)

I've seen this clue in The Globe and Mail.

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