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