In Michigan my parents (each from other parts of the country) used both interchangeably, but they were Silent Generation, so I grew up knowing that dinner is actually what lunch used to be called and supper is the evening meal (and usually significantly lighter; dinner was the main meal, basically). I’ve had people comment that this is a Southern thing, but it isn’t; my father was born and raised in NYC after his parents immigrated there, and in his youth in the 1930s and 1940s, fancier places like restaurants and fancy-schmancy trains would have a menu listing dinner (heavier meal) and supper (lighter meal), each sometimes served only during certain hours.

Not to confuse things, but there was also ‘luncheon’, now called lunch, which was a lighter meal that fell between breakfast and dinner (your heavier meal; supper might be taken still, or omitted, depending on your life-style. Conceivably, one might choose to eat breakfast, then luncheon a few hours later, then dinner, and then supper, but remember that all of that — including dinner — would be at portions that modern Americans far exceed at every meal. So we’re not talking about a full-on, Cheesecake Factory-quantity of food at every meal. And, adding to that, the four-meal-a-day schedule was more aspirational than actual; overwhelmingly, it tended to be the upper class who took luncheon and they may have opted to do so because a social or work schedule prevented eating much breakfast, and they were going to refrain from eating again until a light supper, skipping dinner entirely, for instance.

If you asked for the luncheon or supper menu, or telling someone about your luncheon or supper, you’d be explaining both the quantity (just a little) and the timing (midday or later towards evening).