They keep together but may be cut back (4)
I believe the answer is:
pins
'they keep together but may' is the definition.
The definition suggests an adverb but the answer is not.
'cut back' is the wordplay.
'cut' becomes 'snip' (snip means to cut).
'back' is a reversal indicator.
'snip' in reverse letter order is 'PINS'.
'be' is the link.
Can you help me to learn more?
(Other definitions for pins that I've seen before include "security codes" , "Wire fasteners" , "Stocking fillers" , "With needles, they create a tingling sensation" .)