The words English sir, Spanish señor, and French monsieur, are all words that you are probably acquainted with. They all share the same Latin origin. The English word sir is found in the English language since about the year 1300, towards the end of the Middle Ages. It began as a title of honor for a knight or a baronet, as well as for priests until the 17th century. Originally, sir was a spelling variant of the word sire, which could be found in English since the 12th century. The word became a common respectful form of address a few decades later and it is found as a salutation in letters 100 years later, in the early 15th century.
English got the word sire from Old French. Speakers of a dialect of Old French, the Normans, invaded England in the year 1066 and, because of that, the French language had a tremendous influence on the English language for some 300 years (cf. Part I, Chapter 12, §12.1). To this day, we find that close to 30% of English vocabulary comes from one or other variant of French, Norman or Parisian mostly, though sometimes also from Provençal, or southern French, which is quite different and which was a prestigious language in the Middle Ages, later to be overshadowed by northern French. Most of these French words come originally from Latin. However, the form and meaning of these words may have changed a great deal from what they were in Classical Latin by the time English borrowed them from French 1,000 years later.
Old French sire (and thus English sir and its predecessor sire) come from an earlier Old French form *sieire, which is the natural derivation of popular Latin *seior, ultimately derived from classical Latin senior, a noun meaning ‘elderly man’, which in Rome meant a man over 45. A variant of Old French sire was sieur, which descended from the accusative form of Latin senior, namely seniōrem. We will come back to this sieur later, since it is obviously the second part of the French word monsieur.
The source of all these words, as we just saw, was Latin senior, which meant ‘older man’. This Latin word was a comparative adjective (sen-ior). (In English, older is the comparative form of the adjective old.) Latin senior was derived from the adjective senex, containing the root sen‑ (sen-ex), meaning ‘old’. This root sen‑ can be found in other English words, such as senile.
The word senior itself was borrowed into English from written Latin (not through French this time) in the late 13th century. Thus, English sir and English senior come ultimately from the same Latin word senior and are thus a doublet.
Another word that comes from Lat. senior is Spanish señor, a word that translates as ‘sir’, ‘mister’, or ‘lord’, depending on the context. Spanish did not borrow the word señor from Latin, but it is rather a natural, patrimonial development of Latin senior in a language that, unlike English, is a direct descendant of Latin (just like French, Italian, Portuguese and Catalan are direct descendants from Latin).
As for French monsieur (pronounced [məsjø]), which translates as ‘sir’ but also as the title ‘mister’ (‘Mr.’), we have already seen that the sieur part is naturally derived from a particular form of the Latin word senior. The sound changes are the result of word-of-mouth transmission for 1,000 years in what is now northern France. As you can see, French modified Latin words a bit more than Spanish or Italian did. As for the first part, mon, it is nothing but a first person possessive adjective, meaning ‘my’ (it is ultimately derived from Lat. meum, accusative form of the possessive meus ‘my’, the source of Spanish mi and mío). Thus, monsieur originally meant ‘my lord’. If you are or have ever been a Catholic, you may recognize a cognate of French monsieur in English, namely the word monsignor, which is ‘the title of various senior Roman Catholic posts’. It is a loanword from Italian monsignore (mon+signore) and a cognate of French monsieur. The Spanish equivalent is monseñor and the French equivalent is monseigneur, both calques from the Italian word.
Parallel to monsieur in French is the word madame, which (you may have guessed it) originally meant ‘my lady’, since it is formed out of the parts ma ‘my’ (feminine) and dame ‘lady’. The feminine possessive ma is derived from Lat. meam, accusative of the feminine possessive mea, feminine form of Lat. meus. (The Spanish cognate of Fr. ma are the possessives mi and mía.)
French dame comes from Latin domina ‘mistress of a family, wife; owner, etc.’, which was the feminine form of dominus ‘household master, owner, etc’, both derived from Lat. domus ‘house’. Like its masculine form, French madame is equivalent to the title ‘Mrs.’ (which is a reduced form of mistress) in addition to ‘lady’. (Eng. mistress is a 14th century loanword from French maistresse which meant ‘mistress (lover)’, ‘housekeeper’, as well as ‘governess, female teacher’.) English borrowed the word madam from French around the year 1300. In one of the forms of this word, the middle d is typically not pronounced (often written ma’am). Another meaning for this word (in which the d is pronounced) is ‘female owner or manager of a brothel’, a meaning acquired in the late 19th century.
By the way, the source of French madame, namely Latin mea domina, is also the source of Old Italian madonna (equivalent to Standard Italian mia donna), a word originally associated with the Virgin Mary and artistic depictions of her. English borrowed the word madonna from Italian in the 1580s. However, most Americans perhaps think of US entertainer Madonna when they hear this word, however. For this performer, this is actually not just an artistic name, but one that was given her by her parents (it is also the name of her mother, a French Canadian).
As you may have guessed, the female name Donna in English also comes from Italian donna, and thus from Latin domina. English prima donna is just a loanword (phrase, actually) from Italian, where it means ‘first lady’. The term was borrowed into English in 1782 to refer to the ‘the chief female singer in an opera or opera company’ (COED). Fifty years later, the English term acquired a secondary sense ‘a very temperamental and self-important person’ (COED), which is probably the first (or only) meaning that most Americans think of when they hear the word.
We should mention that the word for ‘lady’, and ‘Mrs.’, in Spanish is señora, derived from the masculine señor. Both of these words can be used as titles followed by a last name, as in señora García ‘Mrs. García’ and señor García ‘Mr. García’. They can also be used as nouns meaning ‘lady’ and ‘gentleman’ (as in señoras y señores ‘ladies and gentlemen’).
Finally, since we have mentioned Latin dominus and domina, we should mention that the Spanish titles Don ‘Mr., Mister’ and Doña ‘Mrs.’ are directly derived from those Latin words. (Spanish doña is thus a cognate of the English name Donna.) Unlike the titles Señor and Señora, which are used with last names, Don and Doña are used with first names, as in Don Juan ‘lord John’ (the feminine would be doña Juana ‘lady Jane’). The term don juan, with the meaning ‘philanderer, ladies’ man, womanizer’ was borrowed into English in the 19th century. Its source is the name of a Spanish libertine nobleman, the character in a famous 17th century Spanish play, which was adapted into French and Italian later in the century. It was popularized in English in a poem by Lord Byron written in 1819.