Again one is going back east by train (7)
I believe the answer is:
retinue
'train' is the definition.
(thesaurus)
'again one is going back east' is the wordplay.
'again' becomes 're'.
'one' becomes 'unit' ('unit' can be a synonym of 'one').
'is going back' says the letters should be written backwards.
'east' becomes 'e' ('E' can be a synonym of 'east').
'unit' written backwards gives 'tinu'.
're'+'tinu'+'e'='RETINUE'
'by' is the link.
(Other definitions for retinue that I've seen before include "Attendants, followers" , "Group of assistants" , "Suite of followers" , "VIP's attendants" , "Group around VIP" .)