Prex sacerdotis brevis est.

The subject is prex.

You can tell because prex is in the nominative singular, which is the case Latin normally uses for the subject of a sentence. The verb est is also singular, so it matches prex.

So grammatically:

• prex = subject
• est = verb
• brevis = predicate adjective describing the subject
• sacerdotis = a genitive word modifying prex

Because Latin usually shows possession or close relationship with the genitive.

In English, we often use:

• the priest's prayer
• or the prayer of the priest

Latin uses the genitive for that idea, so sacerdotis means of the priest or the priest's.

The dictionary form is sacerdos (priest), and its genitive singular is sacerdotis.

Because -is here is the genitive singular ending of a third-declension noun.

For sacerdos, sacerdotis:

• nominative singular: sacerdos
• genitive singular: sacerdotis
• genitive plural: sacerdotum

So sacerdotis means of the priest, not of the priests.

Because brevis is a third-declension adjective, and it must agree with prex.

Prex is:

• nominative
• singular
• feminine

So the adjective must also be:

• nominative
• singular
• feminine

For brevis, breve (short), the nominative singular masculine and feminine form is brevis. The neuter form would be breve.

So brevis is exactly the form you would expect with prex.

It describes prex, not sacerdotis.

A very important Latin rule is that an adjective agrees with the noun it describes in:

• gender
• number
• case

Here:

• prex = nominative singular feminine
• brevis = nominative singular feminine

But:

• sacerdotis = genitive singular

Since brevis matches prex, that is the noun it describes.

So the structure is basically:

[prex] [sacerdotis] [brevis] [est]
= [the prayer] [of the priest] [is short]

Because Latin word order is much freer than English word order.

In English, we strongly expect something like the short prayer. Latin does not need to keep the adjective right beside the noun in the same way, because the endings already show what goes with what.

So even though brevis is separated from prex, the agreement makes the relationship clear.

Latin often places words in an order that sounds natural, emphasizes something, or creates a certain rhythm. Here the order is perfectly normal.

Yes. Latin allows several different orders without changing the basic meaning.

For example, you could also have:

• Prex brevis sacerdotis est
• Brevis est prex sacerdotis
• Sacerdotis prex brevis est

These all still mean the same basic thing, though the emphasis or style may change.

That is one of the big differences between Latin and English: in Latin, endings do most of the grammatical work, so word order is more flexible.

Often, yes.

Latin frequently leaves out forms of esse (to be) when the meaning is obvious. So Prex sacerdotis brevis could also be understood as a complete statement in many contexts.

However, est is also very normal, and including it makes the sentence fully explicit.

So:

• Prex sacerdotis brevis est = fully stated
• Prex sacerdotis brevis = also possible in many contexts

Prex is a third-declension feminine noun.

Its dictionary entry is usually given as:

• prex, precis = prayer, request, entreaty

So:

• nominative singular: prex
• genitive singular: precis

The stem is prec-. The nominative singular has -x, which comes from an older combination like -cs.

So even though prex may look unusual at first, it is a real third-declension noun with a normal grammatical explanation.

It is a real and correct Latin word, but learners should know that the plural form preces is often especially common in Latin texts.

So you may see:

• prex = a prayer, a plea
• preces = prayers, pleas, entreaties

That does not make the singular wrong. It just means that, in actual reading, the plural may appear very often.