A sebaceous cyst (3)
I believe the answer is:
wen
'a sebaceous cyst' is the definition.
(I know that sebaceous cyst can be written as wen)
This is the entire clue.
(Other definitions for wen that I've seen before include "Common cyst on the skin" , "Strange new type of wart." , "Sebaceous cyst" , "New sort of tumour" , "Benign tumour on the head, could be new" .)