Way to address lady in Mothers' Union? (5)
I believe the answer is:
madam
'way to address' is the definition.
I can't judge whether this definition defines the answer.
'lady in mothers' union?' is the wordplay.
'lady' becomes 'Ada' (woman's name).
'in' indicates putting letters inside.
'mothers' union?' becomes 'mm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ada' inserted inside 'mm' is 'MADAM'.
Can you help me to learn more?
(Other definitions for madam that I've seen before include "Courteous form of address to a woman" , "precocious schoolgirl?" , "Term of address to a woman" , "formidable woman" , "Leader of House of Congress" .)