La palabra “casa” es un sustantivo femenino en singular.

La palabra means the word. Spanish often uses this structure when talking about a word itself.

So:

• La palabra casa... = The word casa...

Here, palabra is the main noun, and casa is the specific word being discussed.

Because palabra is a feminine noun in Spanish, so it takes the feminine article la.

• la palabra = the word

This is a good reminder that noun gender in Spanish is grammatical. You have to learn the gender of each noun.

Because the sentence is talking about the word casa, not about an actual house.

Compare:

• La casa es grande. = The house is big.
• La palabra casa es un sustantivo femenino. = The word casa is a feminine noun.

Writers often use quotation marks, italics, or bold to show that a word is being mentioned as a word.

Es means is. It is the third person singular form of the verb ser.

• ser = to be
• es = is

So:

• La palabra casa es... = The word casa is...

Because sustantivo is a masculine noun.

• un sustantivo = a noun

Even though the sentence says that casa is feminine, the word sustantivo itself is masculine, so it uses un.

This is an important distinction:

• casa is a feminine noun
• but sustantivo is a masculine word

Sustantivo means noun.

A sustantivo is a word for a person, place, thing, or idea.

Examples:

• casa = house
• libro = book
• mujer = woman

So the sentence is identifying casa as a noun.

Because femenino is describing sustantivo, and sustantivo is masculine singular.

• un sustantivo femenino = a feminine noun

Even though casa is feminine, the adjective must agree with sustantivo, not with casa.

So:

• sustantivo → masculine
• therefore femenino → masculine form

Here, femenino means feminine in grammatical gender.

It does not mean that the object itself is female. A house is not biologically female; casa is simply treated as a feminine noun in Spanish grammar.

That is why you say:

• la casa = the house

not

• el casa

En singular means in the singular form.

That tells you the word is not plural.

• casa = singular
• casas = plural

So the sentence is saying that casa is:

• a noun
• feminine
• singular

Both ideas are understandable, but en singular is a common way to say that a word is in the singular form.

It focuses on the form of the word:

• casa is written en singular
• casas is written en plural

You may also see similar explanations written in other ways, such as:

• La palabra casa es un sustantivo femenino singular.
• La palabra casa está en singular.

All of these communicate roughly the same idea.

If the word were plural, you could say:

• La palabra casas es un sustantivo femenino en plural.

Or more naturally:

• La palabra casas es un sustantivo femenino plural.

Here:

• casas = plural of casa
• it is still feminine
• but now it is plural, not singular

Yes. Spanish grammar marks nouns for gender and number more clearly than English does.

In English, we usually just say:

• House is a singular noun

But in Spanish, you often specify:

• whether the noun is masculine or feminine
• whether it is singular or plural

So this sentence reflects a very common kind of grammar explanation in Spanish.