Although both terms can be used for savoury preparations (meat cakes or vegetable gateaux) their main use is for sweet baked goods.
Cakes can be large or small, plain of fancy, light or rich.
This is due to primarily to advances in technology (more reliable ovens, manufacture/availability of food molds) and ingredient availability (refined sugar). When removed the icing cooled quickly to form a hard, glossy [ice-like] covering.
Since the Second World War, however, usage of the term has honed in on an elaborate 'cream cake': the cake element, generally a fairly unremarkable sponge, is in most cases simply an excuse for lavish layers of cream, and baroque cream and fruit ornamentation...
The word gateau is the modern French descendant of Old French guastel, 'fine bread'; which is probably of Germanic origin.
It was not until the middle of the 19th century that cake as we know it today (made with extra refined white flour and baking powder instead of yeast) arrived on the scene. The Cassell's New Universal Cookery Book [London, 1894] contains a recipe for layer cake, American (p. Butter-cream frostings (using butter, cream, confectioners [powdered] sugar and flavorings) began replacing traditional boiled icings in first few decades 20th century.
In France, Antonin Careme [1784-1833] is considered THE premier historic chef of the modern pastry/cake world.
Most were probably rather sickly, made from cheap sponge filled with 'buttercream'..coated with fondant icing. French gateau are richer than the products of British bakers. These products naturally relaxed into rounded shapes.
They involve thin layers of sponge, usually genoise, or meringue; some are based on choux pastry. The later are rarely dairy cream; instead creme patissiere (confectioner's custard--milk, sugar, egg yolks, and a little flour) or creme au buerre (a rich concoction of egg yolks creamed with sugar syrup and softened butter) are used. By the 17th century, cake hoops (fashioned from metal or wood) were placed on flat pans to effect the shape.Thus Artois had gateau razis, and Bournonnais the ancient tartes de fromage broye, de creme et de moyeau d'oeulz.Hearth cakes are still made in Normandy, Picardy, Poitou and in some provinces in the south of France.Gateau has wider applications in French, just as 'cake' does in English..can mean a savoury cake, a sweet or savoury tart, or a thin pancake." ---Oxford Companion to Food, Alan Davidson [Oxford University Press: Oxford] 1999 (p. Choux/ puff paste, sponge, French cremes, Gateau St. As time progressed, baking pans in various shapes and sizes, became readily available to the general public.Moulded cakes (and fancy ices) reached their zenith in Victorian times.In its northeastern Old French dialect from wasel it as borrowed into English in the thirteenth century, where it survived until the seventeenth century." ---An A to Z of Food and Drink, John Ayto [Oxford University Press: Oxford] 2002 (p.