Notice of passing planet's route not right (4)
I believe the answer is:
obit
'notice of passing' is the definition.
(obituary)
'planet's route not right' is the wordplay.
'planet's route' becomes 'orbit' (I've seen this in another clue).
'not' is a deletion indicator.
'right' becomes 'r' (common abbreviation).
'orbit' with 'r' removed is 'OBIT'.
(Other definitions for obit that I've seen before include "late anniversary" , "Death notice abbreviated" , "Biography after death, in short" , "Passing information" , "19d to remember" .)