Mi hermana siempre cumple su palabra.

In modern standard Spanish, you normally use the short possessive before the noun:

• mi hermana = my sister
• tu casa = your house
• su palabra = his/her/your word

Unlike English, Spanish does not usually combine the + possessive in this position. So la mi hermana sounds wrong in standard modern Spanish.

Spanish does sometimes use the definite article with a possessive in other structures, but not here.

Cumple is the third-person singular present form of the verb cumplir.

The subject is mi hermana, which is she in English, so the verb has to match that subject:

• yo cumplo = I keep / I fulfil
• tú cumples = you keep / you fulfil
• él/ella cumple = he/she keeps / fulfils

So:

• Mi hermana cumple... = My sister keeps...

Here, cumplir means to keep, to fulfil, or to carry out.

In the expression cumplir su palabra, it means:

• to keep one’s word
• to do what one said one would do

This is a very common use of cumplir. The verb can also appear in other expressions, for example:

• cumplir una promesa = to keep/fulfil a promise
• cumplir una obligación = to fulfil an obligation
• cumplir 30 años = to turn 30

So cumplir is a flexible verb, and its exact translation depends on the context.

Because cumplir su palabra is the natural idiomatic expression in Spanish.

English says keep your word, but Spanish uses cumplir rather than a verb meaning keep/store/hold. This is a good example of why word-for-word translation often does not work well between languages.

So although keep in English and cumplir in Spanish are not identical in all situations, in this expression they match naturally:

• keep your word = cumplir tu palabra
• keep his word = cumplir su palabra

Both are possible, but su palabra is the normal, simple way to say it.

• Mi hermana siempre cumple su palabra. = natural and neutral
• Mi hermana siempre cumple la palabra de ella. = understandable, but awkward and unnecessarily heavy in most contexts

Spanish usually prefers a possessive adjective like mi, tu, su, nuestro when the owner is clear.

Also, since the subject is already mi hermana, it is obvious that su refers to her here.

No. Su can mean several things depending on context:

• his
• her
• its
• your (formal singular)
• their
• your (plural, in Spain usually formal, though vuestro is used for informal plural)

In this sentence, because the subject is mi hermana, we understand su palabra as her word.

If there were ambiguity, Spanish could clarify with:

• la palabra de ella = her word
• la palabra de él = his word
• la palabra de ellos = their word

Siempre is an adverb meaning always, and Spanish commonly places adverbs like this before the conjugated verb:

• Mi hermana siempre cumple su palabra.

That is the most neutral and natural order.

You may also hear other placements in some contexts, but this one is standard and very common. Compare:

• Siempre llega temprano. = She always arrives early.
• Siempre dice la verdad. = He/She always tells the truth.

So the placement of siempre here is very typical Spanish word order.

Yes, that is grammatically possible.

• Mi hermana siempre cumple su palabra.
• Mi hermana cumple siempre su palabra.

Both are correct. However, the first version with siempre before the verb is generally the most natural and neutral.

The second version may sound slightly more marked or stylistically different, depending on context and emphasis.

The present tense in Spanish is often used to describe:

• habits
• repeated actions
• general truths
• personal characteristics

So Mi hermana siempre cumple su palabra means that this is her usual behaviour or a stable trait of her character.

It is similar to English:

• My sister always keeps her word.

This is not about one single occasion; it describes what she is like in general.

Yes, palabra literally means word, but in this expression it refers to a person’s word in the sense of a promise, commitment, or what they said they would do.

So although the literal noun is word, the overall meaning is closer to:

• promise
• word of honour
• commitment

That is why cumplir su palabra means to keep one’s word, not just something about vocabulary or speech.

You may encounter cumplir con in other contexts, but for this idiomatic expression, cumplir su palabra is the most direct and standard form.

For example, cumplir con is common in sentences like:

• cumplir con una obligación = to fulfil an obligation
• cumplir con las normas = to comply with the rules

But with palabra, the fixed and natural phrase is usually:

• cumplir su palabra

So for a learner, this is the version to remember.

You place no before the verb:

• Mi hermana no siempre cumple su palabra. = My sister does not always keep her word.
• Mi hermana nunca cumple su palabra. = My sister never keeps her word.

Notice the difference:

• no siempre = not always
• nunca = never

That distinction is important.

You change both the subject and the verb form.

Examples:

• Yo siempre cumplo mi palabra. = I always keep my word.
• Tú siempre cumples tu palabra. = You always keep your word.
• Él siempre cumple su palabra. = He always keeps his word.
• Nosotros siempre cumplimos nuestra palabra. = We always keep our word.
• Ellos siempre cumplen su palabra. = They always keep their word.

This is a useful sentence pattern to practise verb conjugation and possessives at the same time.