The first meal of the day is typically "desayuno."
The typical first meal of the day is called breakfast, which in Spanish is called "desayuno." You can find this information by knowing the order of meals in a typical day and the translations of those meals in Spanish. In general, the order of meals in a day goes: breakfast, lunch, snack, and dinner. "Desayuno" is the word used to refer to breakfast in Spanish-speaking countries, so that would be the correct answer.
