Piece of information I came across in retirement (4)
I believe the answer is:
item
'piece of information' is the definition.
(eg a news item)
'i came across in retirement' is the wordplay.
'came across' becomes 'met' (to come across is to meet or encounter).
'in retirement' says the letters should be written backwards (retire can mean to go back or backwards).
'met' reversed gives 'tem'.
'i'+'tem'='ITEM'
(Other definitions for item that I've seen before include "Record" , "Part of a list" , "Something on list" , "Unit or distinct part" , "Object, detail" .)