Shortest route across the globe merited a shot (8)
I believe the answer is:
diameter
'shortest route across the globe' is the definition.
(direct line across a circle or sphere)
'merited a shot' is the wordplay.
'shot' is an anagram indicator.
'merited'+'a'='meriteda'
'meriteda' anagrammed gives 'DIAMETER'.
(Other definitions for diameter that I've seen before include "Calibre" , "Maximum distance across circle" , "A demerit for line bisecting a circle" , "width of bar" , "Straight line across circle passing through its centre" .)