Today’s idiom: se mettre sur son trente et un

Today we say hello and what on earth do you mean to a new idiom. This time we have: se mettre sur son trente et un / to put on your Sunday best; dressing up to the nines

To be perfectly honest I shouldn’t have picked this idiom because I already know what it means. I know this defeats the object of this blog as a way of learning new idioms, but I’ve always found this a very strange phrase and wanted to know just where it came from.

So just where does this phrase come from?

Apparently back in the medieval period weavers (tisserands) were known to cut back on the amount of thread they used to produce cloth. Rather than sell this on at a lower price as an inferior product they would offer it for the same price as a good quality item.

In between fighting the English and, well, fighting the English again, the French government found time to pass a law that regulated the amount of thread used in each type of cloth. And the highest quality contained 30 x 100 threads and became known as “trentain”. Over time the original meaning of “trentain” has been forgotten and has been replaced by “trente et un”.

And so “putting on your thirty-one” actually refers to putting on a very high quality garment, or as we say in Britain, putting on your Sunday best.