"small room or alcove set aside for meals," 1930, from dine + diminutive (or false French) suffix -ette. Earlier it meant "preliminary dinner, luncheon" (1870).
The Court dinner-hour, in the reign of George III., was at the Hanoverian hour of four o'clock. During the reign of George IV. it gradually crept up to six o'clock, and finally became steady at the Indian hour of seven, and so remained until the reign of Her Most gracious Majesty, when the formal Court dinner-hour became eight o'clock. These innovations on the national hours of meals did not meet the approval of the medical faculty, and in consequence a dinette at two o'clock was prescribed. This has ever since been the favourite Court meal, being in reality a substantial hot repast, which has exploded the old-fashioned luncheon of cold viands. [The Queen newspaper, London, quoted in Imperial Dictionary, 1883]