Also an
acronym for
Unaccompanied Minor on
aeroplane flights.
I was once told by a very nice flight attendant on Air Canada "You've got an UM sitting next to you," upon which I turned to look at the empty seat to my left, and then back at her, quizzically.
"Um?" I said.
"Yes," she said, "an Unaccompanied Minor. She's a twelve-year-old and English, like you." We were flying from London, so it was hardly surprising. "Oh, here she comes" said the attendant, and after some initial fussing over the small, silent girl, who had a mini-sandwich board with UM in big red letters around her neck, she left to go and be nice to some other people. The girl turned out to be going off alone to visit her grandmother in Vancouver, as she had done for the previous three years.
See also Canadians can't help being nice