grammatical number - Plural forms which end in -x such as tableaux

Words borrowed from French and ending in -eau originally had plural forms which appended an -x rather than an -s. For e.g., the plurals of tableau, beau, and plateau were tableaux, beaux, and plateaux respectively. While the use of plateaux and beaux has petered out in favour of plateaus and beaus, tableaux has not.

My questions:

1. How are these -x plural forms pronounced?


2. Is there any particular reason why tableaux is still the preferred plural form unlike plateaux, beaux, and portmanteaux?

Answer

The OED attests as occurring in English texts the following irregular -x noun plurals:

• aboideau > aboideaux


• bandeau > bandeaux


• bateau > bateaux



• bayou > bayoux


• beau > beaux


• bijou > bijoux


• bordereau > bordereaux


• bureau > bureaux


• château > châteaux


• chou > choux


• damoiseau > damoiseaux


• fabliau > fabliaux


• fricandeau > fricandeaux



• jeu > jeux


• lambeau > lambeaux


• maquereau > maquereaux


• morceau > morceaux


• Pineau > Pineaux


• plateau > plateaux


• portmanteau > portmanteaux


• procès verbal > procès verbaux


• réseau > réseaux


• rouleau > rouleaux



• seau > seaux


• tableau > tableaux


• taureau > taureaux


• torteau > torteaux


• Tourangeau > Tourangeaux


• trumeau > trumeaux


• vœu > vœux

Most of those are far too rare to be considered anything other than unassimilated, but of those that aren’t, the Ngrams do not bear out the OP’s assertion that the -x forms have fallen by the wayside. In fact, only the very oldest ones have been superseded by -s forms.

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In the following Ngrams, the -x spelling is in blue and the -s spelling is in red. Notice how the blue nearly always dominates.

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That one is interesting because it is one of the few that shows a distinct difference depending on whether the “British” or “American” corpus has been selected.

British plateaux vs plateaus

American plateaux vs plateaus

Only the French loanwords that have been around longest, and used the most, have lost their irregular inflection. Indeed, one of the very oldest, chapeau is even unattested in the chapeaux form.

On the other hand, words that require special treatment, like châteaux or nouveaux arrivés, can be expected to retain their imported forms longer. It may also be that people who know to use the import as an import, also know to import its irregularity: notice how
vœux, voeux, and voues all occur, but never
vœus. In the same way, there are no instances of châteaus, since if they know enough to hat the a, they surely know enough to -x the plural.