The French term foie gras, from foie, liver, and gras, fat, fatty, denotes the liver of a specially fattened goose or duck prepared as food. Short for pâté de foie gras, it also denotes a smooth rich paste made from fatted goose or duck liver.

Its first known use in English is in The Fudge Family in Paris (1818), by the Irish poet, satirist, composer and political propagandist Thomas Moore (1779-1852). He wrote:

What a place is this Paris!—but stay—
[…] I’ll just sketch a Day,
As we pass it, myself and some comrades I’ve got.
[…]
After dreaming some hours of the land of Cocaigne,
That Elysium of all that is friand and nice,
Where for hail they have bon-bons, and claret for rain,
And the skaiters in winter show off on cream-ice;
Where so ready all nature its cookery yields,
Macaroni au parmesan grows in the fields;
Little birds fly about with the true pheasant taint,
And the geese are all born with a liver complaint.

He added a footnote, in which he alluded to the cruel process

by which the liver of the unfortunate goose is enlarged, in order to produce that richest of all dainties, the foie gras, of which such renowned patés are made at Strasbourg and Toulouse.

French foie is from the Latin noun ficatum, which denoted the liver of an animal fattened on figs. This Latin word is also the origin of the following nouns meaning liver in the other Romance languages:
– Italian fegato,
– Spanish hígado,
– Portuguese fígado,
– Catalan fetge,
– Romanian ficat.

Latin ficatum was a calque of Greek συκωτόν (= sukoton), a past participle meaning fed on figs which was used as a noun meaning the liver of an animal so fatted (Latin also had the noun sycotum, synonym of ficatum).

The word ficatum was derived from the Latin noun ficus, meaning the fruit of the fig-tree, corresponding to Greek σῦκον (= sukon), denoting the fruit of the συκῆ (= suke), i.e. the fruit of the fig-tree. (Via French figue, the English noun fig is from Latin ficus.)

In his encyclopaedia of the natural and human worlds, Naturalis Historia (Natural History – 77), the Roman statesman and scholar Pliny the Elder (23-79) wrote:

Apicius* made the discovery, that we may employ the same artificial method of increasing the size of the liver of the sow, as of that of the goose; it consists in cramming them with dried figs, and when they are fat enough, they are drenched with wine mixed with honey, and immediately killed.

* There were three Romans of this name, celebrated for their skill in gastronomy. The most illustrious of them lived in the reigns of Augustus and Tiberius. A probably spurious treaty is extant, to which his name is attached, titled De Arte Culinaria (On the Art of Cookery). He was mentioned by many other classical writers.