"We have dinner."

Omdat het Engelse diner een plaats is waar je gaat eten, en dus niet iets wat je eet.

'Diner' is a fancy word for referring to dinner. When you go out for dinner or when you're throwing a dinner party, you will use 'diner'. When we're just having regular dinner at home, we're having 'avondeten'.

Likewise, even though the distinction in meanings is not as great (nowadays they are almost used interchangeably), when we're going out for lunch we more often refer to having 'lunch', whereas if we're just eating at home, we're often having either 'middageten' or 'lunch'. :)

From what I remember, in Belgium 'avondmaal' and 'middagmaal' are used often instead.

Then there's also 'avondmaaltijd' and 'middagmaaltijd', but these are not commonly used in everyday conversation, at least in the area I'm from. (:

So, quick recap:

1. Het diner = fancy dinner
2. Het avondeten = normal dinner
3. De lunch = fancy/normal lunch
4. Het middageten = slightly less fancy/normal lunch

Other words you may come across: het avondmaal; de avondmaaltijd; het middagmaal; de middagmaaltijd = literally meaning either 'eveningmeal' or 'afternoonmeal'.