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"En" is a form of "en", a preposition which is often translated as "in". "Una" is a form of "una", a noun which is often translated as "one". Learn more about the difference between "en" and "una" below.
en()
A preposition is a word that indicates the relationship between a noun and another word (e.g., He ran through the door.).
la una()
A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (time)
