Animal arrived then left (5)
I believe the answer is:
camel
'animal' is the definition.
(thesaurus)
'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).
'came'+'l'='CAMEL'
(Other definitions for camel that I've seen before include "Humped ungulate" , "Desert transport" , "It is called the ship of the desert" , "Humped animal" , "African carrier" .)