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"Invierno" is a form of "invierno", a noun which is often translated as "winter". "Mes" is a noun which is often translated as "month". Learn more about the difference between "invierno" and "mes" below.
el invierno()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
1. (season)
a. winter
Los niños usan abrigos gruesos durante el invierno.The kids wear thick coats during the winter.
2. (rainy months) (Andes) (Central America)
Regionalism used in Central America: Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama
a. rainy season
Llegamos a Ecuador en pleno invierno.We arrived in Ecuador in the middle of the rainy season.
el mes()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
a. monthly salary (income)
Recibo mi mes el 30 de cada mes.I get my monthly salary on the 30th of the month.
a. period
No quiere ir a nadar porque está con el mes.She doesn't want to go swimming because she has her period.