Everything one left at the rail terminus (3)
I believe the answer is:
all
'everything' is the definition.
(I've seen this before)
'one left at the rail terminus' is the wordplay.
'one left' becomes 'l' (common abbreviation).
'at' says to put letters next to each other (I've seen this in other clues).
'the rail terminus' becomes 'al' (I am not sure about this - if you are sure you should believe this answer much more).
'l' after 'al' is 'ALL'.
Can you help me to learn more?
(Other definitions for all that I've seen before include "that's as many as there are" , "Entire" , "Passage in a formal garden" , "Everyone - complete" , "The lot, everyone" .)