Beast of burden arrived, then left (5)
I believe the answer is:
'beast of burden' is the definition.
'arrived then left' is the wordplay.
'arrived' becomes 'came' (coming is a kind of arriving).
'then' says to put letters next to each other.
'left' becomes 'l' (common abbreviation).
(Other definitions for camel that I've seen before include "Humped animal", "Bearer of burdens", "Humped beast", "Beastly type", "African carrier".)