La lluvia arruinó la fiesta.

Because both lluvia and fiesta are feminine singular nouns in Spanish, so they normally take the feminine singular article la.

• la lluvia = the rain
• la fiesta = the party

In this sentence, la lluvia is the subject and la fiesta is the direct object.

Also, Spanish uses the definite article more often than English does. So la lluvia is very natural here, even though English might simply say rain in some contexts.

Arruinó is the preterite form, used for a completed action in the past.

So La lluvia arruinó la fiesta means the rain ruined the party as a finished event.

If you said arruinaba, that would be the imperfect, which usually suggests:

• an ongoing or repeated action in the past
• background description
• something habitual

So:

• La lluvia arruinó la fiesta = the rain ruined the party
• La lluvia arruinaba la fiesta = the rain was ruining the party / used to ruin the party

For this sentence, the preterite is the natural choice because it refers to one completed event.

Arruinó is:

• third person singular
• preterite
• from the verb arruinar = to ruin

So it can mean:

• he ruined
• she ruined
• it ruined
• you ruined (formal singular, usted)

In this sentence, it means it ruined, because the subject is la lluvia.

The accent mark shows the correct stress and also helps distinguish forms.

• arruino = I ruin / I am ruining (present)
• arruinó = he/she/it ruined (preterite)

So the written accent is important because it changes both pronunciation and meaning.

Yes. Just like in English, a thing or event can be the subject if it causes the action.

In La lluvia arruinó la fiesta:

• La lluvia = the thing doing the action grammatically
• arruinó = ruined
• la fiesta = what was affected

This is completely normal in Spanish. Other similar examples:

• El viento tiró el árbol. = The wind knocked down the tree.
• El calor me agotó. = The heat exhausted me.

Because la fiesta is a direct object, but it is not a person.

Spanish uses the personal a mainly before specific human direct objects, and sometimes pets or personified beings.

Compare:

• La lluvia arruinó la fiesta. = no a, because la fiesta is a thing
• Vi a María. = a is used because María is a person

So a is not needed here.

Yes, but the original order is the most neutral and natural.

Standard order:

• La lluvia arruinó la fiesta.

You could also say:

• Arruinó la fiesta la lluvia.

But that sounds marked or literary, and it puts extra focus on la lluvia. In normal conversation, the original sentence is best.

Yes, that is grammatically correct. It is the passive version:

• La lluvia arruinó la fiesta. = active
• La fiesta fue arruinada por la lluvia. = passive

But in Spanish, the active sentence is usually more natural and more common. The passive with fue arruinada por sounds more formal or heavier.

So learners should usually prefer:

• La lluvia arruinó la fiesta.

Arruinar usually means to ruin, to spoil badly, or to wreck something.

In this sentence, it suggests the rain spoiled the party significantly, not just a little.

Depending on context, Spanish also has other verbs with slightly different shades of meaning:

• estropear = to spoil, damage, mess up
• fastidiar = to mess up, annoy
• echar a perder = to ruin, spoil

So arruinar is a strong and clear choice here.

In most of Spain, lluvia is pronounced approximately like YOO-bya, with the stress on the first syllable.

A rough guide:

• llu- sounds like yu-
• -via sounds like -bya

More precisely, in much of modern Spain the ll is pronounced similarly to y. So lluvia and a hypothetical word with yuvia would sound the same in most accents.

The v in Spanish is not pronounced like a strong English v. It is usually a softer sound, often close to b.

In most contexts, it will be understood as referring to a specific party that both speaker and listener can identify from context.

• La fiesta = the party

Even if English might sometimes say Rain ruined the party, Spanish naturally uses the article here.

If you wanted a more general statement, you would usually change the sentence more clearly, for example:

• La lluvia puede arruinar una fiesta. = Rain can ruin a party.

So the original sentence most naturally describes one past event.

No, that sounds wrong in standard Spanish.

Spanish generally needs articles here:

• La lluvia arruinó la fiesta.

Leaving them out would sound unnatural because lluvia and fiesta are being used as normal countable/reference nouns, not in some special headline style.

Spanish allows article omission in certain cases, but not in a normal sentence like this one.

You put no before the verb:

• La lluvia no arruinó la fiesta. = The rain didn’t ruin the party.

That is the normal way to negate a simple sentence in Spanish.

The structure is:

• subject + no
  • verb + object

So:

• La lluvia
  • no
    • arruinó
      • la fiesta