Palindromic term of address (4)
(Other definitions for maam that I've seen before include "Formal address to a lady" , "HRH" , "Lady's address" , "Polite address to Queen" , "Form of address to the Queen" .)
'palindromic term of address' 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 "'Call Me ---' (I. Berlin)" , "Polite form of address for a woman" , "Make wildly happy" , "pompous young lady?" , "Stuck-up girl" .)