Flap as night flyer returns (3)
I believe the answer is:
tab
'flap' is the definition.
(both can mean a small piece of material)
'night flyer returns' is the wordplay.
'night flyer' becomes 'bat' (bats fly at night).
'returns' says the letters should be written backwards.
'bat' back-to-front is 'TAB'.
'as' acts as a link.
(Other definitions for tab that I've seen before include "Small flap - bill" , "ticket" , "Running bar bill" , "Text indent key" , "Flap; illicit drug pill (slang)" .)