I just read an online article where the writer used the term 'nonplused'.

It didn't make sense to me in the context. So I pointed out in the comments section that the writer is using the term incorrectly.

ie. nonplused means literally 'no more' = speechless, at a loss for words

Someone else pointed out that language evolves and lately a new specifically 'North American' meaning has developed and it means
'unperturbed'.

Now it strikes me as odd that a new meaning would emerge that actually contradicts the old. So I may have to ask people what they mean when they use that term. Maybe Im going too far, but it also seems to me this new meaning is just ignorant, like using a word without fully understanding it.   Just because a lot of people write 'must of' instead of 'must have' (or could of instead of could have) does not make it right.

Any thoughts? And Yes I'm North American too, and when I think back, I probably thought nonplused meant 'unperturbed' until someone pointed it out.
Petr