Groups travelling together across deserts (8)
I believe the answer is:
caravans
'groups travelling together across deserts' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for caravans that I've seen before include "Travellers" , "Processions of camels crossing the desert" , "Processions of camels travelling together in single file" , "Vehicles with living quarters" , "Campers equipped with living quarters" .)