This word better belongs in works about fables rather than lexicons. Barometz (also often spelled borametz) is another name for the vegetable lamb of Tartary.
Therein lies a tale. Long ago and far away, in a mysterious place called Scythia that lay on the northern shores of the Black Sea in the territory of the Tartars, there was said to grow a tree of miraculous form. It was described in a French book of about 1357 which purported to be the recollections of an English knight, Sir John Mandeville, though it was actually a compilation of travel stories from classical and medieval times put together by a Benedictine monk who probably never travelled further than his monastery’s library. (Many works continue to claim he was a real person. However, the Dictionary of National Biography has an entry for him that makes clear he’s fictional. He joins a select company of myth figures in the DNB that includes Britannia, Merlin, Robin Hood, John Bull, Ned Ludd, the Unknown Warrior and Piltdown Man.) The travel work became popular and was translated into at least ten languages. This is the description of the plant from a much later English translation:
There groweth a sort of Fruit as it were Gourds, and when it is ripe, Men cut it asunder, and they find therein a Beast as it were of flesh, bone and blood, as it were a little Lamb without Wool, and Men eat the Beast and Fruit also, and sure it seemeth very strange.
The Voyages and Travels of Sir John Mandevile, Knight; Wherein is set down the Way to the Holy Land, and to Hierusalem: as also to the Lands of the Great Caan, and of Prestor John; to India, and divers other Countries: Together with many and strange Marvels therein, London, 1727.
The story was later embroidered to suggest that the beast was a real lamb, which was linked to the plant by an umbilical stem so that it could browse on nearby vegetation. When all was consumed, the lamb died. The story is often supported by the assertion that barometz was a Tartar word meaning “lamb”, difficult to check because Tartary was a vast and poorly-defined region of central Asia with many languages. The Oxford English Dictionary suggests instead that it’s from Russian baranets for a species of club-moss, the link perhaps being that the Russian word is a diminutive of baran, a ram.
Travellers’ tales were often so much embroidered that only a wide-eyed innocent could believe them. But a kernel of truth frequently lay buried within them. In this case, the source was works by the classical authors Herodotus (“Certain trees bear for their fruit fleeces surpassing those of sheep in beauty and excellence”) and Pliny (“These trees bear gourds the size of a quince which burst when ripe and display balls of wool out of which the inhabitants make cloths like valuable linen”). The barometz was almost certainly cotton, native to India.
Jamie Greenbaum told me about a related legend. “In a delightful coincidence from the other end of the continent, the Chinese were bamboozled by cotton for centuries. Early in the thirteenth century Genghis Khan summoned a Chinese Taoist leader to his base in Central Asia. A disciple of the Taoist later published a record of the journey and it was translated by Arthur Waley some 80 years ago under the title The Travels of an Alchemist. A footnote by Waley reads: ‘The Chinese, being unfamiliar with cotton, could not believe that a stuff was obtained by cultivating a tree, and imagined that a lamb, being buried, produced a crop of fresh lambs next year. This legend can be traced back in China to the sixth century. Allusions to it are frequent in Chinese literature.’”