In Spanish, nouns have two genders: masculine and feminine. Most of masculine nouns end in -o.
El niño (the boy)
El gato (the cat)
El libro (the book)
El vaso (the glass)
El bolígrafo (the pen)
Exception: la mano (the hand) is feminine.
Most of feminine nouns end in -a.
La niña (the girl)
La gata (the female cat)
La silla (the chair)
La botella (the bottle)
La montaña (the mountain)
-words that end in -ma and -ta.
el planeta (the planet), el atleta (the athlete), el poeta (the poet).
-other nouns like el día (the day), el mapa (the map).
Nouns that end in -e or with a consonant can be masculine or feminine:
-Masculine: the days of the week – lunes (monday), martes (tuesday), miercoles (wednesday), jueves (thursday), viernes (friday).
numbers: dos (two), tres (three), siete (seven), nueve (nine), diez (ten)
other nouns: el coche (the car), el restaurante (the restaurant), el café (the coffee), el papel (the paper), el árbol (the tree), el amor (the love), el pan (the loaf of bread).
-Feminine: nouns that end in –ción and –sión – la canción (the song), la acción (the action), la televisión (the TV), la ilusión (the illusion).
the letters of the alphabet: la efe (eff), la eme (em), la ene (en), la hache (aitch), la ese (ess).
other nouns: la noche (the night), la gente (the people), la nieve (the snow), la leche (the milk), la universidad (the university), la nariz (the nose), la luz (the light).
How to form the feminine of the nouns in Spanish?
-Nouns that end in -o replace it with -a.
El gato (the cat) – La gata (the female cat)
El niño (the boy) – La niña (the girl)
El hermano (the brother) – La hermana (the sister)
-Nouns that end with a consonant add -a.
El profesor (the professor) -La profesora (the female professor)
El director (the director) – La directora (the female director)
El señor (the man) – La señora (the woman)
-Nouns that end in -e don’t change.
El estudiante (the student) – La estudiante (the female student)
El paciente (the patient) – La paciente (the female patient)
El cantante (the singer) – La cantante (the female singer)
-Some nouns constitute the feminine form with other endings:
El actor (the actor) – La actriz (the actress)
El rey (the king) – La reina (the queen)
El principe (the prince) – La princesa (the princess)
-Some nouns are completely different in the masculine and in the feminine form.
Padre (father) – Madre (mother)
Hombre (man) – Mujer (woman)
Yerno (son-in-law) – Nuera (daughter-in-law)
Caballo (horse) – Yegua (female horse)