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"La líder" is a form of "líder", a noun which is often translated as "leader". "El" is a form of "el", a definite article which is often translated as "the". Learn more about the difference between "la líder" and "el" below.
el líder, la líder, líder(
lee
-
dehr
)This means that the noun can be masculine or feminine, depending on the gender of the noun it refers to (e.g., el doctor, la doctora).
An adjective is a word that describes a noun (e.g., the big dog).
2. (preeminent)
el(
ehl
)A definite article is a word that identifies a noun as specific or known to the speaker (e.g., the girl).