Some compound words do, however, like firetruck. It's a truck. For fire. Breakfast falls into that category.
I don't disagree with the it started as first meal of the day regardless of time of day, but these days it is more likely to mean morning meal than it is first meal of the day.
You could refer to the concept of breakfast, the meal, and also the common food of breakfast, bacon and eggs, with the same word.