Servae mensam in triclinio ad cenam instruunt.

Because instruunt is third person plural: they set/prepare. The form servae can, in theory, mean several things:

• nominative plural = female slaves / maidservants
• genitive singular = of the female slave
• dative singular = to/for the female slave

But only nominative plural fits naturally with the plural verb instruunt. So here servae is the subject: the female slaves / maidservants.

Mensam is accusative singular of mensa.

It is the direct object of instruunt, so it answers the question What are they setting/preparing?
Answer: the table.

This is very typical in Latin: the thing directly affected by the verb goes into the accusative.

Because in can take two different cases, depending on the meaning:

• in + ablative = in / on a place, showing location
• in + accusative = into / onto a place, showing motion toward

Here the sentence means the table is being set in the dining room, so it gives location, not movement. Therefore Latin uses the ablative:

• triclinio = ablative singular

If the meaning were into the dining room, you would expect in triclinium.

Ad cenam literally means for dinner or for the meal.

• ad takes the accusative
• cenam is accusative singular of cena

Here ad expresses purpose or reference: the table is being prepared for dinner.

So this is not mainly about motion; it is about what the preparation is for.

Instruunt is:

• present tense
• active voice
• indicative mood
• third person plural

It comes from instruere, which can mean things like:

• arrange
• equip
• prepare
• set out

In this context, with mensam, it means set/prepare the table.

Classical Latin normally has no articles like English the or a/an.

So:

• servae can mean the female slaves or female slaves
• mensam can mean the table or a table
• triclinio can mean the dining room or a dining room

You decide from context what sounds best in English. Latin simply does not need articles in the way English does.

Latin word order is much freer than English word order because Latin uses case endings to show how words function.

In English, word order does most of the work:

• The girls set the table is different from
• The table sets the girls

In Latin, the endings already show who is doing what:

• servae = subject
• mensam = object

So Latin can arrange words more flexibly.
This sentence has a very natural Latin order:

• Servae = subject
• mensam = object
• in triclinio = place
• ad cenam = purpose
• instruunt = verb at the end

Putting the verb at the end is especially common in Latin.

By form alone, yes: servae can be genitive singular.

But in this sentence that reading does not work well. If you tried to take it as of the female slave, you would still need a clear subject for instruunt (they prepare), and there is no better candidate. Also, servae mensam would not naturally mean the female slave’s table in this context.

So grammar and sense together point strongly to servae as nominative plural.

Triclinium is a Latin noun meaning dining room. Historically, it referred to a Roman dining room with three couches for reclining at meals.

It is a second-declension neuter noun:

• nominative singular: triclinium
• ablative singular: triclinio

Its gender is simply part of the noun’s lexical identity. In Latin, nouns belong to grammatical genders, and those genders do not always match anything logical or natural.

Both can be reasonable, depending on context.

• serva literally means a female slave
• In some teaching contexts, people use maidservant because it sounds smoother in English
• In a Roman household context, slave is often the more historically accurate word

So grammatically, servae just means the plural of serva; the best English wording depends on how literal or historical you want to be.

Good question. Cenam is accusative not because it is the direct object of instruunt, but because it is the object of the preposition ad.

Many Latin prepositions require a specific case.
Here:

• ad always takes the accusative

So in ad cenam, the accusative comes from the preposition, not from the verb.

Yes, very often.

Because the endings show the grammar, Latin can move words around without changing the basic meaning. For example, these would still mean essentially the same thing:

• Mensam servae in triclinio ad cenam instruunt.
• In triclinio servae mensam ad cenam instruunt.
• Ad cenam servae mensam in triclinio instruunt.

However, the emphasis can shift slightly depending on what comes first or last. The original order is a perfectly normal, straightforward Latin sentence.