The pronunciation of the word is indeed the irregular
[məsjø], not naively
[mɔ̃sjœr] (though historically it seems to have been the very first way of saying it, then
[mɔsjø], then the modern one). I never heard the
[misjø] you’re referring to.
Monseigneur is pronounced regularly, like the words that compose the expression Mon seigneur (so :
About the reason that could explain this odd pronunciation, there’s a few explanations here, there and even there, but I guess it’s not very satisfying or definitive. Anyway, euphony is probably one of the reasons it changed, because the term is one of the most heavily-employed of the language, considering the modern pronunciation is slightly quicker.
Maybe are you speaking about messieurs, it’s the plural of monsieur, or developed, this could come from mes seigneurs → mes sieurs.
This could be pronounced like
mae see eu (not
eu does not have an equivalent in English.
Or maybe you are hearing some joke, as some aim to represent the outlander spoken French of a
- South African: missié, spoken like
- North African: missiou, spoken like
- Chinese: missie, spoken like
The question of the actual pronunciation of both monsieur and monseigneur need not be asked, but I will try and answer the other part of the question, i.e. why is the combination of the letters (o+n) pronounced differently in each word.
I’ll start by quoting David Crystal “Languages are always in a state of flux… the most noticeable and frequent changes affect pronunciation and vocabulary…”.
Vowel sounds are more prone to evolution than consonants. I suppose it is because phonatory organs are not as easily controlled when sounding vowels than when sounding consonants (just a hint, but the question could be asked on linguistics Stack Exchange1.
Another factor in pronunciation evolution is the question of the stressed syllables. Vowels will change more easily when unstressed.
Now, back to monsieur and monseigneur. Both are a combination of the possessive mon + sieur or seigneur, and both were written as two separate words that concatenated as the French language evolved.
When said as two separate words (mon+sieur), had two equally stressed syllables. But as the words evolved into one single entity with a shift in meaning and the loss of the understanding of the original meaning (including the fact that mon was no longer perceived as a possessive) the first syllable became unstressed (French words are regularly stressed on the last syllable), the nasal /ɔ̃/ evolved into the unstressed vowel sound /ə/.
In monseigneur, even when concatenated into one single word the mon has always retained its possessive meaning (I suppose we could say that French people still perceive the word monseigneur as the English perceive my lord), and even nowadays when we say the word we tend to have an auxiliary stress on the first syllable, thus the original /ɔ̃/ sound remaining unchanged.
For more on the evolution of vowel pronunciation in the French language one could have a look at the wikipedia article on Old French and at this book: Introduction à la phonétique historique du français
by Annick Englebert for a study of the historical evolution of French pronunciation.
1 I asked the question on Linguistics and got very interesting answers.
You need to say mon like when you say in french me
for exemple: “je me suis fait mal”
Then sieur like when you say in french si and yeux
for exemple: “Si tu viens, je viens” and “tu as de beaux yeux”
ME-SI-YEUX → Monsieur
I think it’s pronounced /məsjø/ because that is easier than /mɔ̃.sjø/.
Okay so to give an actual simple answer to this question, it just seems to be an incorrect pronunciation that’s become popularized in urban culture. More accurately, what it could be is people taking the plural word messieurs and thinking that the singular form of that would be messieur instead of monsieur. Either way it’s wrong but that’s where I believe it comes from.