Old character — one's a bit prickly (5)
I believe the answer is:
thorn
This clue is a double definition.
'old character' is the first definition.
(letter used in Old English)
'one's a bit prickly' is the second definition.
(Other definitions for thorn that I've seen before include "eg Prickle on rose" , "source of discomfort" , "causing sharp irritation" , "Pointed growth" , "irritation when in one's side" .)