Gather in from the terminus, possibly (6)
I believe the answer is:
muster
'gather' is the definition.
(mustering is a kind of gathering)
'in from the terminus possibly' is the wordplay.
'from' indicates named letters should be taken away.
'possibly' is an anagram indicator.
'terminus' with 'in' removed is 'termus'.
'termus' with letters rearranged gives 'MUSTER'.
(Other definitions for muster that I've seen before include "marshal" , "a lot of peacocks" , "Mobilize" , "Assemble, gather together" , "Assemble for duty" .)