Skin growth (4)
I believe the answer is:
wart
'skin growth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for wart that I've seen before include "Abnormal blemish on the skin, caused by a virus" , "Verruca" , "Horny skin growth" , "Small hard excrescence on the skin" , "Small rounded protuberance on the skin" .)