From The Oxford English Dictionary The Definitive Record of the English Language
(On-line resource from library)
Dessert
Etymology: < French dessert (Estienne 1539) ‘removal of the dishes, dessert’, < desservir to remove what has been served, to clear (the table), < des-, Latin dis- + servir to serve.
a. A course of fruit, sweetmeats, etc. served after a dinner or supper; ‘the last course at an entertainment’ (Johnson).
b. ‘In the United States often used to include pies, puddings, and other sweet dishes’ ( Cent. Dict.). Now also in British usage.
Dinner
The chief meal of the day, eaten originally, and still by the majority of people, about the middle of the day (cf. German Mittagsessen), but now, by the professional and fashionable classes, usually in the evening; particularly, a formally arranged meal of various courses; a repast given publicly in honour of some one, or to celebrate some event.
Supper
The last meal of the day; (contextually) the time at which this is eaten, supper time. Also: the food eaten at such a meal. Often without article, demonstrative, possessive, or other modifier.
The time and style of ‘supper’ varies according to history, geography, and social factors. For much of its history, ‘supper’ was simply the last of three daily meals (breakfast, dinner, and supper), whether constituting the main meal or not. In the United States, ‘supper’ is now a less frequent synonym for ‘dinner’ as the evening meal. Where both ‘supper’and ‘dinner’ can be applied to the last of three meals, supper is often a lighter or less formal affair than dinner (though see sense 2b). Where four meals a day are recognized, ‘supper’ is a light late meal or snack following an early evening dinner or a late afternoon or early evening ‘tea’.
In America a lot of people have always said supper.