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"Besides" is a preposition which is often translated as "además de", and "furthermore" is an adverb which is often translated as "además". Learn more about the difference between "besides" and "furthermore" below.
besides()
A preposition is a word that indicates the relationship between a noun and another word (e.g., He ran through the door.).
1. (apart from)
a. además de
Besides the toiletries, I have to buy a new bathing suit for the trip.Además de los artículos de tocador, tengo que comprar un nuevo traje de baño para el viaje.
furthermore()
An adverb is a word that describes a verb, an adjective, or other adverbs (e.g., to run quickly, very tired).
1. (moreover)