Characteristic group of symptoms (8)
I believe the answer is:
syndrome
'characteristic group of symptoms' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for syndrome that I've seen before include "Set of symptoms indicating disease" , "Set of symptoms indicating abnormal conditions" , "Particular group of symptoms that always occur together" , "Set of linked symptoms" , "Group of linked symptoms" .)