Mum has boy who may belong to secret society (5)
I believe the answer is:
mason
'mum has boy who may belong to secret society' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'mum has boy' is the wordplay.
'mum' becomes 'ma' (both can mean mother).
'has' says to put letters next to each other.
'boy' becomes 'son' (male child).
'ma'+'son'='MASON'
Can you help me to learn more?
(Other definitions for mason that I've seen before include "A worker in stone - may be free" , "US comedian" , "one in construction" , "Stone carver" , "Stone-worker" .)