Not much can be in an enclosure! (6)
I believe the answer is:
scanty
'not much' is the definition.
Both the answer and definition are adjectives. Maybe there's an association between them I don't understand?
'can be in an enclosure' is the wordplay.
'be in' is an insertion indicator.
'an enclosure' becomes 'sty' (sty is a kind of enclosure).
'can' put within 'sty' is 'SCANTY'.
Can you help me to learn more?
(Other definitions for scanty that I've seen before include "Spare" , "Insufficient in amount" , "Inadequate" , "Of small amount, barely enough" , "Too small or little" .)