LE SAVIEZ-VOUS ?

Trentain (portez du) et soyez
« sur votre trente-et-un » !

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        (D’après « Dictionnaire des curieux : complément pittoresque
et original des divers dictionnaires » paru en 1880 et « Histoire
de l’industrie française et des gens de métiers » (Tome 1) paru en 1872)

Se mettre sur son trente-et-un, c’est se mettre en grande toilette pour rendre une visite, assister à un baptême, à une noce, etc.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Mais savez-vous que dans cette expression, "Trente-et-un" ou "Trente-un" est une corruption de "Trentain" ? 

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Au Moyen Age, des règlements fort sévères punissaient, non seulement les ouvriers qui avaient employé dans leur fabrication des matières premières avariées, mais encore ceux qui ne donnaient pas à leurs produits les formes et les dimensions requises.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             En ce qui concernait les tisserands en laine, ces règlements allaient jusqu’à fixer le nombre des fils dont devait se composer la trame. 

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  On trouve à ce sujet des détails curieux dans le tome 1 de l’Histoire de l’industrie française d’Alexis Monteil.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Le collage de la chaîne, le foulage, le feutrage, le soufrage, le calendrage, tout est prévu, sans oublier la longueur et la largeur de la pièce ; et « si le tisserand donnait des dimensions moindres à ces pièces, que lui arriverait-il ?

« Il aurait le poing coupé ; et c’est bien fait, tant pis pour les voleurs : les honnêtes tisserands ont toujours voulu conserver leurs deux mains pour dire le chapelet. »

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          Suivant la qualité des draps, la trame devait se composer de quatorze cents ou de dix-huit cents fils.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     Pour le drap fin destiné aux vêtements de luxe, le nombre des fils était de trente fois cent fils ; ce qui fit donner à drape le nom de trentain. 

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Porter du trentain était donc le fait d’un homme riche qui ne regardait pas aux dépenses de toilette.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Trentain, terme technique, se métamorphosa facilement en trente-un dans la bouche de ceux qui ne connaissaient pas l’origine de cette appellation ; et, l’usage ayant prévalu de dire trente-et-un, ces mots sont restés pour désigner une toilette soignée.