Traditional funeral unvarying, in essence, due to planned route (9)
I believe the answer is:
itinerary
'planned route' is the definition.
(I've seen this before)
'traditional funeral unvarying in essence' is the wordplay.
I cannot quite understand how this works, but
'in' is found in the answer.
This explanation may well be incorrect...
'due to' is the link.
Can you help me to learn more?
(Other definitions for itinerary that I've seen before include "Planned route" , "Travel plan" , "Record of a journey" , "Tiny airer? (anagram)" , "schedule" .)