Thing I encountered on the way back (4)
I believe the answer is:
item
'thing' is the definition.
(thesaurus)
'i encountered on the way back' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'on the way back' shows that the letters should be reversed in order.
'met' written backwards gives 'tem'.
'i'+'tem'='ITEM'
(Other definitions for item that I've seen before include "Element" , "Single article on a list" , "Particular" , "Matter" , "One unit on a list" .)