One thing I met on the way back (4)
I believe the answer is:
item
'one thing' is the definition.
(an item is a thing)
'i met on the way back' is the wordplay.
'on the way back' shows that the letters should be reversed in order.
'met' reversed gives 'tem'.
'i'+'tem'='ITEM'
(Other definitions for item that I've seen before include "Unit; detail" , "Record" , "couple linked" , "One article" , "Individual object" .)