Expression of disapproval that unnerves talker initially (3)
I believe the answer is:
tut
'expression of disapproval' is the definition.
(I've seen this before)
'that unnerves talker initially' is the wordplay.
'initially' indicates taking the first letters.
The first letters of 'that unnerves talker' is 'TUT'.
(Other definitions for tut that I've seen before include "Show disapproval" , "Exclamation of disapproval or annoyance" , "That's bad!" , "I disapprove" , "Sound disapproving" .)