Subject twitching about work (5)
I believe the answer is:
topic
'subject' is the definition.
('topic' can be a synonym of 'subject')
'twitching about work' is the wordplay.
'twitching' becomes 'tic' (tic is a kind of twitching).
'about' is an insertion indicator.
'work' becomes 'op' (abbreviation for opus).
'tic' going around 'op' is 'TOPIC'.
(Other definitions for topic that I've seen before include "Matter for an argument" , "A subject for conversation or debate" , "Subject (of a talk, etc)" , "Subject (eg, of text)" , "might this be hot?" .)