This time, not so much an uncommon word as an entertaining use, from Walden; or, Life in the Woods by Henry David Thoreau: sinecure. Thoreau writes that he has, for many years, been "self-appointed inspector of snowstorms and rain storms", kept paths clear after storms, looked after escaped animals, and watered plants during dry seasons:
In short, I went on thus for a long time (I may say it without boasting), faithfully minding my business, till it became more and more evident that my townsmen would not after all admit me into the list of town officers, nor make my place a sinecure with a moderate allowance.
This one might be particularly familiar to those interested in politics; it refers to a job that requires no work, but still offers payment or other benefits. In Thoreau's case, he means that the townsfolk refused to pay him for the work he was already doing for free.
According to the Corpus of Contemporary American English, sinecure appears about once in eighteen million words in modern American English in general, and about once in three million words in news magazines. Strangely, it occurs nearly that often in science fiction and fantasy, too. Fairly rare, but positively common compared to some of the archaisms to be found in literature. More of those to come!