Breakfast

Strictly, the first meal of the day, even when not eaten in the morning.

Derived from the words break and fast. In this case, to break the fast between the last meal of the previous day and the first meal of the current day.

Joe: I'm eating breakfast.

Jane: It's 6PM. The sun is going down.

Joe: I haven't eaten today. I'm breaking a fast.

Jane: I'm leaving you.