Spanish - Nouns

After nouns: Adjectives

Adjectives usually come after the noun they are describing.

E.g.

un vestido azul (a blue dress)
una camisa roja (a red shirt)

Before nouns

Words like first, second, next, last go before the noun:

el primer piso
la tercera puerta
la próxima semana
la última semana

Gender

All nouns are either masculine or feminine.

masculine: nouns often end in -o, use el, e.g. el niño (the boy)
feminine: nouns often end in -a, use la, e.g. la niña (the girl)

Nouns end in consonants:

masculine: l, r. E.g. hospital, tenedor.
feminine: pared, habitación, televisión, costumbre, luz.

Languages and days of the week are always masculine, no matter the ending letter.

The endings of adjectives depend on the gender of what they describe.

E.g. americano (male) / americana (female)

When -o and -a rule is broken:

Words that are shortened versions of other words. For example, la foto (photograph) is feminine because it's short for la fotografía.
Words that end in -ista, e.g. dentista can be either masculine or feminine.
Words whose meanings vary depending on the gender. For example, un cometa is a comet, but una cometa is a kite.
Some masculine words that come from Greek and end in -a (often -ma). Most of these words have English cognates.
A few compound nouns, which are traditionally masculine, even when the noun portion comes from a feminine noun.
Words that are just exceptions, such as mano and día. Usually these exceptions come from the way the words were treated in Latin.
el agua (water) and el águila (eagle)—feminine words that begin with a stressed a- or ha- and are immediately preceded by el (rather than la) in the singular form only. With these words, el doesn't indicate gender but is used instead for ease of pronunciation. It is similar to the way in which English substitutes "an" for "a" in front of some nouns, as the rule applies to the opening sound of the word, not how it's spelled.

Examples:

el día: day
el drama: drama
el idioma: language
la mano: hand
el mañana: near future (but la mañana, tomorrow or morning)
el mapa: map
el papa: pope / la papa: potato
el policía: policeman
el problema: problem
la radio: radio
el sistema:system
el sofá: sofa

Some words can be either masculine or feminie, like "estudiante" (el estudiante or la estudiantte). These words are often referred to as "epicene nouns". These words use the same form for both masculine and feminine, and the gender is typically determined by the article ("el" or "la") or other context clues within the sentence.

Professions & Roles:

el/la artista (artist)
el/la cantante (singer)
el/la jefe/a (boss)
el/la periodista (journalist)
el/la presidente/a (president)

People:

el/la bebé (baby)
el/la joven (young person)
el/la testigo (witness)
el/la víctima (victim)

Other:

el/la agente (agent)
el/la cliente (client)
el/la estudiante (student)
el/la paciente (patient)
el/la personaje (character)

Plural

Just like in English, add -s or -es (if the word ends in a consonant) to the end of the word.

libro => libros
el bolígrafo => los bolígrafos
la carta => las cartas
las mujeres

If a word ends in -z (e.g. lapiz, pez, feliz), remove the -z and add -ces to make it plural.

el pez => los peces
la vaca feliz => las vacas felices

Add -s / -es to both nouns and adjectives

el zapato verde => los zapatos verdes

Also mi / tu / su

mi / tu / su camisa => mis / tus / sus camisas

Agreement

Words describing a noun should agree in their gender:

un / el niño mexicano
una / la niña mexicaa

Occupations

The word changes depending on the gender of the person

maestro / maestra: teacher
profesor / profesora: professor
médico / médica: doctor

el agua

El is often used for masculine nouns and la for feminine ones. But when the noun begins with a stressed a- or ha-, you must use el regardless of the gender.