Birthmark (6)
(Other definitions for naevus that I've seen before include "A red-purple birthmark" , "disfiguring mark" , "A red birthmark on skin" , "A red-coloured birthmark" , "A scarlet birthmark on skin" .)
'birthmark' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mole that I've seen before include "digger" , "one in the Underworld?" , "Heap of soil (a 6 mountain?)" , "Skin spot; breakwater" , "Agent; breakwater" .)