Originally, “flatware” meant not cutlery but dishes—that is, “plates, dishes, saucers and the like, collectively,” in the words of the Oxford English Dictionary.
Such things were called “flatware” in the mid-19th century to distinguish them from “holloware” (or “hollow-ware”), a 17th-century term for bowls, cups, pots, pans, and other vessels with some depth to them, mostly made of metal.
The word “flatware” was first recorded, according to the OED, in the official catalogue for the Great Exhibition of 1851, which carried this description:
“Plates, dishes, saucers, &c., termed ‘flat ware,’ are made from moulds which form the inside of the article, the exterior being given by ‘profiles’ of the required outline, made of fired clay, glazed.”
But by the end of the century “flatware” was being used—especially in the US—to mean “domestic cutlery,” the OED says. All four of the dictionary’s citations are American, and show that “flatware” could be made of silver.
Oxford’s earliest example is from an 1895 Montgomery Ward catalogue: “Solid Sterling Flat Ware … Tea Spoons … Dessert Forks … Sugar Shells … Butter Knives.”
A few years later, in 1901, the New York Evening Post carried a reference to “a complete line of Rogers Flatware.”
The American author Gertrude Atherton used the term in her 1914 novel Perch of the Devil: “A magnificent silver service, from many dozens of ‘flat ware,’ to silver platters.”
And Mary McCarthy used it in her 1952 novel The Groves of Academe: “She seemed to fix her eyes on the flatware and napery with the same hypnotized effort that dragged her fork to her lips and back again.” (Earlier, we were told the table had been laid with a lace cloth and “wedding silver.”)
Today, many people use “flatware” to mean any kind of cutlery, and reserve “silverware” (another term coined in the mid-19th century) for tableware made of silver or an alloy of silver.
But this isn’t universally the case. In our experience, people sometimes use “silverware” loosely to mean knives, forks, and spoons in general.
“Tableware,” by the way, is a general term for articles used at the table—“cutlery, crockery, etc.,” as the OED says. It was first recorded in the late 1700s.
“Ware” in all these compounds, Oxford says, is a collective term for “articles of merchandise or manufacture; the things which a merchant, tradesman, or pedlar, has to sell; goods, commodities.”
This Germanic word, first recorded in English around the year 1000, is also used in the plural, as when we speak of a shopkeeper’s “wares.”
But etymologists think it may be older yet in English, and that it could be the same word as a now defunct “ware” from the 800s.
This obsolete word, first recorded in the ninth century, meant “watchful care,” “safekeeping,” and the like, and is the source of “wary,” “beware,” and “aware.”
So the 11th-century version of “ware” meaning goods, the OED suggests, is “used in the concrete sense ‘object of care.’ ”
As for plastic knives, forks, and spoons, we’d call them “plastic knives, forks, and spoons,” but some googling suggests that “plastic cutlery” is the preferred term among the people who make and sell the stuff.
Although the term “cutlery” has traditionally referred to knives, scissors, and other cutting implements since it entered English in the 1400s (via the Old French coutelerie), many standard dictionaries now accept its use for knives, forks, and spoons.