Symbol of stubbornness (4)
I believe the answer is:
mule
'symbol of stubbornness' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mule that I've seen before include "Drug courier; animal" , "Obstinate quadruped" , "The animal said to be stubborn" , "Obstinate person?" , "Hybrid beast" .)