Madam
noun [ S ]
formal uk/ˈmædəm/ usa formal and polite way of speaking to a woman:
May I carry your cases for you, Madam?
Dear Madam
the usual way of beginning a formal letter to a woman whose name you do not know:
Dear Madam, I am writing to enquire about ...
Madam Minister/President/Secretary/Speaker, etc.
POLITICS
the official title used when speaking to a woman who has a senior position in a government:
Madam Secretary, are there any circumstances under which the United States would agree to this policy?
Compare
Sir