Desert animal (5)
'desert animal' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for camel that I've seen before include "Yellowish" , "One travelling in caravan" , "Dromedary, perhaps" , "Saddle animal in desert regions" , "It is called the ship of the desert" .)
I believe this clue is a double definition.
'desert' is the first definition.
(abandon treacherously)
'animal?' is the second definition.
(rat is a kind of animal)
(Other definitions for rat that I've seen before include "Plague-carrying rodent" , "Rodent pest" , "that gets out of stricken vessel" , "Inform" , "Change sides" .)