Literal Translation
To put oneself on one’s 31
Actual Meaning
To dress up to the nines? I think!
Etymology
While the first part of this expression can be easily explained (‘mettre sur soi’ = ‘to get dressed’), the origin of the expression and the number ‘31’ remains a mystery to many authors and literary figures.
There are various interpretations, ranging from a distortion of the word
“trentain”, which referred to a high-quality fabric. At the time, owning a garment made from this fabric was a luxury, and therefore something reserved for special occasions. However, the dates of use of this word up to the 15th century and the official appearance of the expression in the 19th century do not match.
Another explanation suggests that it refers to a forgotten number on a ceremonial military uniform, or an unexplained reduction from thirty-six, as in “se mettre sur son trente-six” (to dress up).
A third variant comes from Prussia, where the 31st of the month was a golden day for soldiers because they were paid a bonus to finish the month, the “supplement d’entretien” (maintenance allowance). As the 31st only appeared seven times a year, it was celebrated! Visits were organised to the barracks, where soldiers had to look their best and might even find a match.
A final possibility came from a card game that was very popular in the 19th century: thirty-one. Reaching the number thirty-one
meant winning and was considered the best possible outcome.