I'd seem odd in passing (6)
I believe the answer is:
demise
'passing' is the definition.
(I've seen this before)
'i'd seem odd' is the wordplay.
'odd' is an anagram indicator.
'id'+'seem'='idseem'
'idseem' is an anagram of 'DEMISE'.
'in' acts as a link.
(Other definitions for demise that I've seen before include "(Person's) death" , "Death, collapse" , "Passing" , "Death or termination" , "The end of something" .)