Mother and boy cursed (6)
I believe the answer is:
damned
'cursed' is the definition.
(synonyms)
'mother and boy' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'and' means one lot of letters go next to another.
'boy' becomes 'ned' ().
'dam'+'ned'='DAMNED'
(Other definitions for damned that I've seen before include "Consigned to everlasting punishment" , "Abominable" , "Condemned to Hell" , "Cursed" , "Mad Ned was doomed" .)