Wonderful group of friends that takes the longest route round the world (5,6)
I believe the answer is:
great circle
'the longest route round the world' is the definition.
(largest circle around a sphere)
'wonderful group of friends' is the wordplay.
'wonderful' becomes 'great' (I've seen this before).
'group of friends' becomes 'circle' (I've seen this before).
'great'+'circle'='GREAT CIRCLE'
'that takes' is the link.
(Other definitions for great circle that I've seen before include "Navigation by spherical arc" , "short course for pilots" , "shortest way, by plane" , "that goes right round the globe" , "The equator is one for the earth" .)