Today my in-laws are providing Thanksgiving Dinner. Or is it lunch? We will be eating at noon. Gene Bob wants to know about the whole supper vs dinner thingee, which surprises me because he's from Mifipi and I thought they taught this in Sunday School.
Anyway, for those needing a remedial education, here's the deal: if you live in a rural community or in the South (including Mifipi), then the noon-day meal is called "dinner" and the evening meal is called "supper". Most others call them "lunch" and "dinner". Why? Because they do.
Oh, you want to get into the entomological roots of the words? You may regret it later. Some authorities think that "dinner" as a mid-day meal entered Middle English lexicon as a nounification of the French word "diner" (but with a feminine little hat over the 'i'), which meant to dine. The French verb, in turn, has latin roots which basically mean to un-fast. In other words, to eat the first (big) meal of the day. Interestingly enough, the early French dined in the morning and it was typically their biggest meal of the day. Even more interestingly, the modern English word "breakfast" has the same meaning.
Even more fascinating is that the word "supper" also appeared in Middle English to describe the evening meal and also has French roots from a verb which means "to eat the evening meal".
Over time, the term dinner has migrated to the evening meal among the urban crowd, possibly because the biggest meal of the day migrated to the evening. Similarly, among the snooty crowd, supper appears to have migrated to be a very late, light, meal, such as after going to the theater. In rural areas, however, where the noon meal was still a large meal, dinner stayed at noon and supper, which started out as a small evening meal, stayed supper but got larger.
So to the early French dinner was breakfast and supper was dinner, or supper. Got it? Thus endeth the lesson.