Originally Posted by rod2024
Even funnier when they show up in mass

We borrowed the phrase en masse from the French: “The mob marched en masse to the Bastille.” It does indeed mean “in a mass,” and you can use that English expression if you prefer, but “in mass” is an error.May 24, 2016

in mass | Common Errors in English Usage and More

Washington State University
https://brians.wsu.edu › 2016/05/24 › in-mass