In a book I’m reading, the narration uses the word nonplussed in a way that implies that it means a character is unbothered by something.
I initially assumed that was a diction mistake, but I checked my dictionary just to be sure, and was astonished to find, in addition to the traditional meaning, a second definition:
2. chiefly US : not bothered, surprised, or impressed by something
There’s an explanatory note:
The use of nonplussed to mean "unimpressed" is an Americanism that has become increasingly common in recent decades and now appears frequently in published writing. It apparently arose from confusion over the meaning of nonplussed in ambiguous contexts, and it continues to be widely regarded as an error.
I’ve never seen this usage before, and even though I’m usually more or less a descriptivist, I hereby go on record as being opposed to this usage.
But I imagine that I’ll eventually get used to it.