Decimus dies longus est.

Decimus means tenth, while decem means ten.

So:

• decem dies = ten days
• decimus dies = the tenth day

In this sentence, Latin needs an ordinal number (first, second, third, tenth) because it is talking about position in a sequence, not quantity.

Dies is in the nominative singular.

It is nominative because it is the subject of the sentence: the day is the thing being described.

You can see the basic structure as:

• Decimus dies = the subject
• longus est = what is being said about the subject

So dies is the word that matches English day as the subject of is long.

Because both words agree with dies.

In Latin, adjectives must agree with the noun they describe in:

• gender
• number
• case

Here, dies is treated as:

• masculine
• singular
• nominative

So the adjectives also appear in the masculine nominative singular form:

• decimus = tenth
• longus = long

That is why they both end in -us.

Good question. Dies is an unusual noun because it is usually masculine, but it can sometimes be feminine in certain contexts.

In a simple sentence like this one, dies is normally masculine, so Latin uses:

• decimus dies
• longus est

If it were feminine, the adjectives would look different, such as decima and longa.

For beginners, the safest rule is: dies is usually masculine.

Latin normally has no definite article and no indefinite article.

So Latin does not have separate words exactly like:

• the
• a
• an

That means decimus dies can mean:

• the tenth day
• sometimes just tenth day, depending on context

English usually requires an article, but Latin often leaves that idea to context.

Est is the third-person singular form of esse, meaning to be.

So:

• est = is

In normal prose, Latin usually includes est in a sentence like this:

• Decimus dies longus est. = The tenth day is long.

Sometimes Latin, especially poetry or very compressed style, can leave out a form of to be when it is easily understood. But for a standard beginner sentence, including est is completely normal.

Latin word order is more flexible than English word order.

Here:

• decimus comes before dies
• longus comes after dies

That is perfectly normal in Latin.

A few helpful points:

• decimus is closely tied to dies, almost like a label: the tenth day
• longus is a predicate adjective, linked through est: is long

So the sentence naturally divides into:

• Decimus dies = the tenth day
• longus est = is long

Latin could sometimes rearrange these words for style or emphasis, but this order is very straightforward.

Yes. Latin allows much more flexibility than English because endings show the grammatical relationships.

For example, these could still mean essentially the same thing:

• Decimus dies longus est
• Longus est decimus dies
• Dies decimus longus est

However, word order can change emphasis or style. The version you have is a very clear, beginner-friendly order.

It is describing dies, but specifically as a predicate adjective.

There are two common ways adjectives work:

1. Attributive adjective: directly attached to a noun

   • dies longus = the long day

2. Predicate adjective: linked to the noun by to be

   • dies longus est = the day is long

In your sentence, longus is a predicate adjective because it goes with est.

A common classroom pronunciation would be roughly:

DEH-ki-moos DEE-ays LON-goos est

More specifically:

• Decimus = DEH-ki-moos
• dies = DEE-ays
• longus = LON-goos
• est = est

A few useful notes:

• c in Latin is always hard, like k
• g is always hard, as in go
• di-es has two vowel sounds, not one

Pronunciation systems vary a little, but that version will serve well for most learners.

The dictionary forms are:

• decimus — ordinal adjective meaning tenth
• dies, diei — noun meaning day
• longus, longa, longum — adjective meaning long
• sum, esse, fui — verb meaning to be; est is one form of this verb

This is useful because Latin dictionaries usually list:

• nouns with nominative + genitive
• adjectives with their masculine/feminine/neuter forms
• verbs with their principal parts

In other contexts, dies can also refer to things like:

• a day
• a date
• a time
• sometimes even a metaphorical appointed day

But in this simple sentence, the basic meaning day is clearly the right one.

So a beginner should understand dies here simply as day.

The sentence follows a very common Latin pattern:

subject + predicate adjective + form of esse

So here:

• Decimus dies = subject
• longus = predicate adjective
• est = is

In other words:

• The tenth day
  • long
    • is

That is why the full sense is The tenth day is long.