This appears in The Penguin Book of Curious and Interesting Words (first published in the USA as the Oxter English Dictonary). Its compiler, George Saussy, quoted from Winter’s Tale, a futuristic work of magical realism of 1983 by Mark Helprin. Mr Helprin defined it as meaning “delicate in motion, graceful and muffled as in the quiet sound made by ballet slippers. Only to be used in winter and at night.” It’s a delightful description. Mr Saussy tells me he included it because it was far superior to the obscurity and fell implications of the definition that appears in the Oxford English Dictionary, in which sober work it is explained as relating to a gallows or hanging.
The word is from Latin patibulum, originally a fork-shaped yoke that was put on the necks of criminals or a fork-shaped gibbet in the shape of a vertical letter Y. It could also mean the horizontal bar of the crucifixion cross, or a forked prop to support vines.
Despite the solemn and religious associations its etymology brings to mind, the Oxford English Dictionary says that patibulary has mainly been used humorously in English. That’s based on citations such as this one, from the Sporting Magazine in 1801: “A certain Corn-Buyer, which had undergone the discipline of a patibulary suspension on a gallows.” But others were deathly serious: in The French Revolution (1837) Thomas Carlyle wrote of the gibbet as “the grim Patibulary Fork ‘forty feet high’”.
The word is now extremely rare. There’s one known appearance in a work by Samuel Beckett (“the patibulary melancholy of the lemon of lemons”) and an occasional historical reference, such as this in a book by Edward Payson Evans about the curious habit of executing animals for supposed crimes: “Hangmen often indulged in capricious and supererogatory cruelty in the exercise of their patibulary functions.”