Today, dinner almost universally refers to the evening meal. But it has had a long etymological history to get to that point.

Those with older relatives might have noticed them say “dinner” to refer to the midday meal—what we would usually call “lunch” today. It’s rather archaic today, but it used to be the dominant usage.

It comes to modern English from Old French disner (via Middle English dyner), which originally meant “breakfast”, but later meant “lunch”. Disner is evolved into modern French dîner, suggesting the same more recent history has taken place in that language as in English.

Disner comes, ultimately, from Latin *disiūnō, meaning “to break the fast”.

So, depending on when you are, “dinner”, and its etymological ancestors, could have meant breakfast, lunch, or dinner.