Words Like "Fortnight"

The word "fortnight" (another way of saying two weeks or 14 days) is an example of a word which was previously used in the US, but which has fallen into disuse, even though it is still commonly used in the UK. I had some doubts regarding the word "trousers" which is British parlance for what we call "pants" (a fact which the British may find amusing since pants are only worn in public by drunken hooligans or in those strange recurring dreams that some people have!), because I wasn't sure if that term was ever used in the US. From what I was able to gather from my research, the words trousers and pantaloons (the latter coming to English from Italian by way of French) briefly co-existed in the US during the 19th century; however, the former quickly fell into disuse in America in favor of pantaloons which was eventually shortenened to pants. Apparently, the first American writer to use the word pants (in the American sense of the word) was Edgar Allen Poe. Even so, most Americans (at least of my generation, I can't be sure concerning the young people of the 21st century!) know what the word trousers means, even if we never use it. Apparently, Mick Jagger was confident of this, when in 1969 he said to his audience in New York, "I think I've just busted a button of my trousers. I hope they don't fall down. You don't want my trousers to fall down now, do ya?!"
In like manner, some words which are still commonly used in the US have fallen into disuse in the UK (for example, the word fall [meaning autumn] according to Christopher Davies in his book Divided by a Common Language: A Guide to British and American English, Houghton Mifflin, 1997, p.3).

I welcome comments and input from my American and British friends regarding this topic. Please also let me know if you can think of more examples of other words which have fallen into to disuse either in the US or in the UK.