Involuntary movement made by tense member of coven (6)
I believe the answer is:
twitch
'involuntary movement' is the definition.
(an involuntary jerking movement)
'by tense member of coven' is the wordplay.
'by' is a charade indicator (letters next to each other).
'tense' becomes 't' (abbreviation used in many dictionaries).
'member of coven' becomes 'witch' (a coven is a group of witches).
't' next to 'witch' is 'TWITCH'.
'made' acts as a link.
(Other definitions for twitch that I've seen before include "Sudden muscular spasm" , "grass" , "involuntary response" , "Quiver spasmodically as in tic" , "Sudden jerky movement; pang" .)