Relation seen in sordid article ostracised (5)
I believe the answer is:
apart
'ostracised' is the definition.
(I've seen this in another clue)
'relation seen in sordid article' is the wordplay.
'relation' becomes 'pa' (pa is a kind of relation).
'seen in' is an insertion indicator.
'sordid article' becomes 'art' (abbreviation for article. I am not sure about the 'sordid' bit.).
'pa' going within 'art' is 'APART'.
Can you help me to learn more?
(Other definitions for apart that I've seen before include "First Christmas present from my love" , "In pieces; separate" , "away" , "Separate in a trap" , "Separated physically" .)