Writhe (6)
I believe the answer is:
squirm
'writhe' is the definition.
(synonyms)
This is all the clue.
(Other definitions for squirm that I've seen before include "feel awkward" , "Twist when struggling" , "'Wriggle, writhe (6)'" , "Wriggle in discomfort" , "Wriggle uncomfortably" .)