Route ends in New Guinea possibly (3)
I believe the answer is:
way
'route' is the definition.
(way is a kind of route)
'ends in new guinea possibly' is the wordplay.
'ends in' suggests the final letters.
The final letters of 'new guinea possibly' are 'WAY'.
(Other definitions for way that I've seen before include "Path" , "Route; direction" , "Method; route" , "Street" , "'Manner, mode (3)'" .)