Perturb, discompose (8)
I believe the answer is:
unsettle
This clue is a double definition.
'perturb' is the first definition.
(thesaurus)
'discompose' is the second definition.
(unsettling is a kind of discomposing)
(Other definitions for unsettle that I've seen before include "Make uneasy, disturb the calm of" , "Nettle us so as to disturb" , "'Disturb, unnerve (8)'" , "Trouble" , "Faze" .)