There is a commune in France near the Somme which has a one letter name. Which letter is it?

Y is a commune in the Somme department in Hauts-de-France in northern France.

Y bears the shortest place name in France, and one of the shortest in the world. The inhabitants call themselves Ypsilonien(ne)s, from the Greek letter Upsilon which looks like the letter Y.

The commune is a level of administrative division in the French Republic. French communes are roughly equivalent to civil townships and incorporated municipalities in the United States or Gemeinden in Germany. The United Kingdom has no exact equivalent, as communes resemble districts in urban areas, but are closer to parishes in rural areas where districts are much larger. Communes are based on historical geographic communities or villages and have received significant powers of governance to manage the populations and land of the geographic area covered. The communes are the fourth-level administrative divisions of France.

A French commune may be a city of 2.2 million inhabitants like Paris, a town of 10,000 people, or just a 10-person hamlet. Communes typically are based on pre-existing villages and facilitate local governance.