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"Año" is a form of "año", a noun which is often translated as "year". "Mes" is a noun which is often translated as "month". Learn more about the difference between "mes" and "año" below.
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.
el año()
A masculine noun is used with masculine articles and adjectives (e.g., el hombre guapo, el sol amarillo).
2. (of school)
a. grade
Si fallo el examen, tendré que repetir el año.If I fail this test, I will have to repeat the grade.