Monarch working to get in style over a long time (7)
I believe the answer is:
chronic
'style over a long time' is the definition.
I can't tell whether this definition defines the answer.
'monarch working to get in' is the wordplay.
'monarch' becomes 'R' (abbreviation for rex, king in Latin).
'working' becomes 'on' (on can mean working or activated).
'to get' means one lot of letters goes inside another.
'in' becomes 'chic' (in can mean chic or fashionable).
'r'+'on'='ron'
'ron' inserted into 'chic' is 'CHRONIC'.
Can you help me to learn more?
(Other definitions for chronic that I've seen before include "(Of an illness) persistent" , "Long-lasting, pain perhaps" , "Deep-seated - long-lasting" , "Very serious" , "pants" .)