Type of train exits eastern line (6)
I believe the answer is:
diesel
'type of train' is the definition.
(diesel train is a type of train)
'exits eastern line' is the wordplay.
'exits' becomes 'dies' ('die' can be a synonym of 'exit').
'eastern' becomes 'e'.
'line' becomes 'l'.
'dies'+'e'+'l'='DIESEL'
(Other definitions for diesel that I've seen before include "Derv" , "Fuel used by heavy vehicles" , "Vehicle fuel" , "Liquid fuel" , "Engine fuel" .)