It shuts when one goes off (6)
I believe the answer is:
eyelid
'it shuts when one goes off' is the definition.
The definition suggests a singular noun which matches the answer.
'it shuts when one' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
'when' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'one' could be 'li' (I've seen this in other clues) and 'li' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for eyelid that I've seen before include "Ocular covering" , "Natural optic covering" , "Optic membrane" , "Batting membrane?" , "Drop it and you cannot see" .)