The following post is from DAILY WRITING TIPS website and details the permutations of abbreviations for courtesy titles. I thought it very interesting and hope you will too.

Mister developed as a variant of master. (Interestingly, the newer title came to pertain to married men, while master, once a title of respect for a social superior, was reserved for unmarried men and boys.) Originally, both master and mister were abbreviated Mr. before a person’s name as a courtesy title, but as master fell out of use, Mr. came to be applied solely as an abbreviation for mister.

Mrs. was originally a generic abbreviation of mistress before a name, but it developed into a courtesy title specifically for a married or widowed woman, while Miss, with no abbreviation, was adopted as an honorific for unmarried women. Ms. began as a variant abbreviation of mistress as a courtesy title in the 1600s but fell out of favor. (At the turn of the twentieth century, it was proposed as a substitute form of address for a woman whose marital status is unknown, but the idea did not gain traction, nor did the abbreviation catch on fifty years later when a couple of business publications brought the issue up again. However, after feminist and journalist Gloria Steinem adopted the abbreviation as the title of a new magazine for women in 1972, its use quickly spread.)

Because no native plural form of Mr. or Mrs. developed in English, the French abbreviations Messrs. (Messieurs) and Mmes. (Mesdames) were borrowed; Mses. developed in imitation, and the plural form of Miss, Misses, like the singular form, did not acquire an abbreviation. Because of the decline in use of such honorifics, the plural forms are rarely seen anymore.

As a reference to a man who embodies a certain quality, Mr. appears in such references as “Mr. Right” (the ideal man for a woman to marry) or “Mr. Big” (a man of significant authority and/or status). Missus, a derivative of mistress based on a casual pronunciation of the latter word, and Miz, a spelling based on the pronunciation of Mrs. or Miss in the southern United States, should generally be used only in dialogue in historically or geographically appropriate fiction. However, “the Mrs.” or “the missus,” spelled as shown as humorous references to one’s wife, are appropriate in informal writing.

I hope you learned something new, for I did!