Begin to wince (5)
I believe the answer is:
start
I believe this is a double definition.
'begin' is the first definition.
(I know that begin can be written as start)
'wince' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for start that I've seen before include "Set in motion" , "Onset" , "get under way" , "Origin" , "Jump suddenly" .)