Unnerve (6)
'unnerve' is the definition.
(I know that unnerve is a more specific form of rattle)
This is all the clue.
(Other definitions for rattle that I've seen before include "Make someone nervous or anxious" , "Child's noisy toy" , "Vibrate noisily" , "Let rat make the sound" , "Noisy toy and snake" .)
'unnerve' is the definition.
(I know that unnerve can be written as faze)
This is the entire clue.
(Other definitions for faze that I've seen before include "disconcerting" , "Put off" , "Throw from" , "Fluster, daunt" , "Unsettle - perturb" .)
(Other definitions for dishearten that I've seen before include "Put a damper on" , "Bring down" , "dismay?" , "cast down" , "Cause (someone) to lose confidence" .)