Brief moment absorbing work matter (5)
I believe the answer is:
topic
'matter' is the definition.
(synonyms)
'brief moment absorbing work' is the wordplay.
'brief moment' becomes 'tic' (I can't explain this - if you can you should give a lot more credence to this answer).
'absorbing' indicates putting letters inside.
'work' becomes 'op' (common abbreviation for 'opus').
'tic' going around 'op' is 'TOPIC'.
(Other definitions for topic that I've seen before include "Matter for an argument" , "Theme of discourse" , "Something to discuss" , "Subject (eg, of text)" , "That may be debatable" .)