My DH insists on calling the meal we have in the evening tea. Fine by me but I've always referred to it as dinner.
So here are my definitions of mealtimes in the order of the day
Breakfast - obvious
Lunch - again obvious I'd have thought
Dinner - the main meal anytime after 5pm
Supper - a bit of toast watching the news
Variations
Tea - a cup of tea or an early main meal consisting of one course with lots of bread and cakes
Brunch - when you get up too late for normal breakfast time and are too early for lunch.
I know dinner time is sometimes referred to as lunchtime i.e. dinner ladies at school but again I'd have thought this was a throw back to when it was probably the main meal of the day.