Collecting nightgear, perhaps (9)
I believe the answer is:
'collecting' is the definition.
(I know that gathering is a type of collecting)
'nightgear perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'nightgear' with letters rearranged gives 'GATHERING'.
(Other definitions for gathering that I've seen before include "convention?" , "Harvesting" , "Assembly, meeting" , "bee" , "Collecting" .)