The term “breakfast” for the first meal of the day first came into use in the English language in the 15th century, before this, the word “disner” was used which meant “to break a fast,” essentially to break the fast of the night before. This is reflected in the modern word for breakfast (break-fast). To make matters more confusing, the meal that became breakfast in English was originally eaten around lunch time. Eventually, as the word breakfast displaced the French-derived disner, the earlier word eventually evolved into the modern word “dinner” which is now the last meal of the day. Before this, the last meal of the day was supper.
Suffice to say, the word breakfast has a confusing history, but it is essentially a literal translation of the French word disner, meaning that the name for the first meal of the day technically has not changed. We still break our nightly fast at breakfast as it was done in the Middle Ages, just at an earlier time during the day.