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"En" is a form of "en", a preposition which is often translated as "in". "Tren" is a noun which is often translated as "train". Learn more about the difference between "tren" and "en" below.
el tren(
trehn
)A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
en(
ehn
)A preposition is a word that indicates the relationship between a noun and another word (e.g., He ran through the door.).