Gather in a New England state, briefly (5)
I believe the answer is:
amass
'gather in' is the definition.
'a new england state briefly' is the wordplay.
'new england state briefly' becomes 'mass' (abbreviation for Massachusetts; 'briefly' asks for an abbreviation).
'a'+'mass'='AMASS'
(Other definitions for amass that I've seen before include "Collect or gather" , "Gather together, pile up" , "Sodium chloride" , "Collect, hoard" , "Accrue, heap up" .)