Which meal do you call which? I am in the strange position that at home I call them lunch and dinner but when I go back to my parents I still use dinner and tea.
It's dinner and tea for me, although strangely if I go out with a friend for a meal at midday I say we are going out for lunch.
I guess it's because we noramlly have the main meal at midday and sandwiches in the evening, so I think your main meal is normally your dinner, but maybe thats just me.
Dinner is the main meal of the day whenever you have it.
If you are a wage slave and you're employer doesn't allow a 2 hour break during the day, then obviously it will have to be in the evening, while you have a crappy sandwich between 12 and 2 to keep you going.
It is healthier and better to eat the largest meal of the day around midday.