Dental cavities (6)
I believe the answer is:
caries
'dental cavities' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for caries that I've seen before include "Decay in bones or teeth (6)" , "Dental cavities" , "Decayed areas in teeth" , "I scare easily with tooth decay" , "Decayed area in a tooth" .)