Possibly reunites trains (8)
I believe the answer is:
retinues
'trains' is the definition.
(I've seen this before)
'possibly reunites' is the wordplay.
'possibly' indicates anagramming the letters.
'reunites' is an anagram of 'RETINUES'.
(Other definitions for retinues that I've seen before include "trains" , "Bands of followers or attendants" , "Groups of advisers etc. accompanying an important person" , "Reunites with following groups" , "Reunites with groups of attendants" .)