Mensor longitudinem metitur.

The subject is mensor.

You can tell because mensor is in the nominative singular, the case normally used for the subject of a sentence. It means the measurer or the surveyor.

So mensor is the one doing the action.

Because longitudinem is in the accusative singular, which marks it as the direct object.

It is the thing being measured.

The basic dictionary form is longitudo meaning length. This is a third-declension noun, and its accusative singular form is longitudinem.

So:

• longitudo = length
• longitudinem = length, as the object of the verb

Because metitur comes from a deponent verb: metior.

A deponent verb looks passive in form, but has an active meaning. So although metitur looks like it might mean is measured, it actually means measures.

This is one of the most important things to learn about Latin verbs:
some verbs have passive-looking endings but active meanings.

Metitur is:

• present tense
• third person singular
• indicative mood

So it means:

• he measures
• she measures
• it measures
• or more generally is measuring

In this sentence, with mensor as the subject, it means the surveyor measures.

Because both the noun and the verb are singular.

• mensor = one surveyor / one measurer
• metitur = he/she/it measures, not they measure

If the subject were plural, the verb would also be plural.

Because the subject must be in the nominative, not the accusative.

• mensor = nominative singular, used for the subject
• mensorem = accusative singular, which would normally be used for a direct object

Since the surveyor is doing the action, Latin uses mensor.

Yes. A deponent verb can still govern a direct object just like an ordinary active verb, if that is how the verb works.

Here, metitur means measures, and it takes the object longitudinem.

So even though the form looks passive, the grammar of the sentence is active:

• mensor = subject
• longitudinem = direct object
• metitur = active meaning, measures

They are usually given as:

• mensor, mensoris = measurer, surveyor
• longitudo, longitudinis = length
• metior, metiri, mensus sum = measure

These dictionary forms help you identify the declension or conjugation and recognize other forms of the same word.

For example:

• longitudinem comes from longitudo
• metitur comes from metior

Not as much as in English.

Latin word order is more flexible because the endings show each word’s job in the sentence. So the sentence could also be written in other ways, such as:

• Longitudinem mensor metitur
• Metitur mensor longitudinem

All of these still mean the same basic thing, because:

• mensor is nominative
• longitudinem is accusative
• metitur is the verb

That said, the original order is perfectly normal and straightforward.

Yes. They are closely related in meaning.

• metitur = measures
• mensor = measurer, one who measures

So mensor is essentially an agent noun built from the same verbal idea.

This is similar to English patterns like:

• teach → teacher
• write → writer

Latin often does the same sort of thing.

A common classroom pronunciation would be roughly:

MEN-sor long-gi-TOO-di-nem ME-ti-toor

A more classical-style pronunciation would treat ti before a vowel more like ti, not like English sh. So metitur is approximately:

ME-ti-toor

And longitudinem is approximately:

lon-gi-TOO-di-nem

The exact pronunciation system can vary depending on whether you are using restored Classical pronunciation or a later school/church tradition.

It can mean either, depending on context.

Latin present tense often covers both ideas:

• measures
• is measuring

So Mensor longitudinem metitur can be understood as either:

• The surveyor measures the length
• The surveyor is measuring the length

Without more context, both are possible.

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

So:

• mensor can mean a surveyor or the surveyor
• longitudinem can mean a length or the length

You decide which English article fits best from the context.