Worry, unnerve (7)
I believe the answer is:
perturb
I believe this is a double definition.
'worry' is the first definition.
(to perturb is to worry or unsettle someone)
'unnerve' is the second definition.
(thesaurus)
(Other definitions for perturb that I've seen before include "Make unsettled" , "Disturb greatly" , "Unsettle, make anxious" , "Opera star" , "Worry" .)