Tiny involuntary convulsion, primarily (3)
I believe the answer is:
tic
'tiny involuntary convulsion primarily' is the definition.
I can't tell whether this defines the answer.
'tiny involuntary convulsion primarily' is the wordplay.
'primarily' indicates taking the first letters.
The initial letters of 'tiny involuntary convulsion' is 'TIC'.
Can you help me to learn more?
(Other definitions for tic that I've seen before include "Jerky movement" , "Convulsion" , "Nervous twitch" , "Facial twitch" , "Muscle twitch" .)