Why is the first world war also called "The Great War"?

The most commonly used name for World War I at the time was The Great War. It was also called the European War and it was often described as “the war to end all wars.”

When it became clear that a second world war was likely, that description no longer seemed accurate and so it became used more and more infrequently. Most historians agree the word “great” was used to indicate the immense scale of the war, meaning how many countries were engaged, how much territory was involved, how many military and civilian casualties happened, how much military equipment took part, and so on.