Sorry about worker shut up inside (9)
I believe the answer is:
repentant
'sorry' is the definition.
(similar in meaning)
'about worker shut up inside' is the wordplay.
'about' becomes 'ret' (I can't justify this - if you can you should believe this answer much more).
'worker' becomes 'ant' (worker is a type of ant).
'shut up' becomes 'pen' (pen can mean to shut in or enclose).
'inside' indicates putting letters inside.
'ret'+'ant'='retant'
'retant' going around 'pen' is 'REPENTANT'.
Can you help me to learn more?
(Other definitions for repentant that I've seen before include "showing contrition" , "Regretful" , "Feeling remorse for misdeeds" , "sorry state" , "Contrite" .)