Sherpa, thankfully, discovered route (4)
I believe the answer is:
path
'route' is the definition.
(I know that route can be written as path)
'sherpa thankfully discovered' is the wordplay.
'discovered' indicates a hidden word (remove the letters covering the answer in the clue).
'PATH' is hidden within 'sherpa thankfully'.
(Other definitions for path that I've seen before include "Walkway" , "Course of action; track" , "Line of travel" , "trail" , "Skin on top of head" .)