Miserable son on notice (3)
I believe the answer is:
sad
'miserable' is the definition.
(similar in meaning)
'son on notice' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'on' means one lot of letters go next to another.
'notice' becomes 'ad' (both can mean an advertisement).
's'+'ad'='SAD'
(Other definitions for sad that I've seen before include "Dismal" , "low" , "Unfortunate" , "Heavy-hearted" , "upset" .)