Palindromic title
(Other definitions for maam that I've seen before include "Lady's address" , "Polite address to Queen" , "Formal address to a lady" , "Royal address" , "Respectful address to the Queen" .)
'palindromic title' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for madam that I've seen before include "Woman of standing" , "What you would call a female customer (or a spoiled girl!)" , "Titled lady" , "precocious schoolgirl?" , "Term of address to a woman" .)