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"La cebolla" is a form of "cebolla", a noun which is often translated as "onion". "Los guisantes" is a form of "guisante", a noun which is often translated as "pea". Learn more about the difference between "la cebolla" and "los guisantes" below.
la cebolla()
A feminine noun is almost always used with feminine articles and adjectives (e.g., la mujer bonita, la luna llena).
1. (vegetable)
a. onion
El cocinero siempre pone cebolla picada en sus tacos.The cook always puts chopped onion in his tacos.
el guisante()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
a. pea
El chef preparó una ensalada de gambas con patatas y guisantes.The chef prepared a shrimp salad with potatoes and peas.