Uncontrollable movement on protest is somewhat common (7)
I believe the answer is:
demotic
'somewhat common' is the definition.
'demotic' can be an answer for 'common' (similar in meaning). I am unsure of the 'somewhat' bit.
'uncontrollable movement on protest' is the wordplay.
'uncontrollable movement' becomes 'tic' (involuntary twitch).
'on' means one lot of letters go next to another.
'protest' becomes 'demo' (demonstration).
'tic' put after 'demo' is 'DEMOTIC'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for demotic that I've seen before include "Of everyday language" , "vulgar?" , "(Of language) used by ordinary people" , "It'd come (anag) - of the common people" , "Colloquial; of the people" .)