1580s, abbreviation of mistress (q.v.), originally in all uses of that word. Prefixed to the name of a married woman by 1610s. The plural Mmes. is an abbreviation of French mesdames, plural of madame, used in English to serve as the plural of Mrs., which is lacking. Pronunciation "missis" was considered vulgar at least into 18c. (compare missus). The Mrs. "one's wife" is from 1920.

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Definitions of Mrs. from WordNet

Mrs. (n.)
a form of address for a married woman;
Synonyms: Mrs