Anonsi, sorry I haven't responded to this post before now, but better late than never.
I think most of the words you mention are dubious as common words. And where there's any serious doubt about a word, it probably should be marked rare. The one exception is
natter - I think this is widely enough used to justify retaining its common status.
A couple of recent examples from popular fiction by US authors:
Well, I guess letting him natter on with his rah-rah pep talk made me feel better.
"Waterbot" by Ben Bova, Analog Science Fiction & Fact, June 2008
The idiot attorney in the gray suit continued to natter on about something useless---the most beneficial way to structure a retirement portfolio or some such rot---but Sullivan Quinn had long since tuned it out.
Wolf at the Door, 2006, by Christine Warren
(Both these quotes courtesy of the
Corpus of Contemporary American English.)
The other three words, though, will be dropped back to rare.
Of the card game faro, Wikipedia says:
It enjoyed great popularity during the 18th century, particularly in England and France, and in the 19th Century in the United States, particularly in the Old West, where it was practiced by faro dealers such as Doc Holliday and Wyatt Earp. It has since fallen out of fashion and is practiced mostly by dedicated Old West enthusiasts and Civil War reenactors.
The word
tarn does seem to be used more in England than the US, although it crops up from time to time in the Colorado-based
Backpacker magazine. Still, I feel it's a fairly specialist word.
Tauten is a standard word, listed in all good dictionaries, but I found no uses at all in the 385 million word Corpus of Contemporary American English, so it seems it's not so common. It gets 10 hits in the British National Corpus, which is not a lot. Incidentally,
tautening was the nine-letter word in the Standard puzzle on 19 April 2006, when only 18% of the players found it.
