This is the 293rd most frequent Spanish word.
principales
"Principales" means "main" or "principal" in English.
In this sentence, 'principales' is functioning as a noun referring to the people in leading positions or authority figures.
Los principales se reunieron para tomar una decisión.
The leaders met to make a decision.
The word 'principales' here is an adjective modifying 'razones' (reasons), implying these are the foremost or primary reasons related to the context of the sentence.
Una de las principales razones fue su dedicación al proyecto.
One of the main reasons was their dedication to the project.
Here, 'principales' is used as an adjective to describe the noun 'temas' (topics), indicating that these topics are the most important or significant in the context of the meeting.