Tooth decay (6)
I believe the answer is:
caries
'tooth decay' is the definition.
(term for decay of a tooth or bone)
This is the entire clue.
(Other definitions for caries that I've seen before include "I scare easily with tooth decay" , "Decayed area in a tooth" , "Dental decay" , "Dental cavities" , "Decayed areas in teeth" .)