Uterque testis verum dicit.

Because uterque is grammatically singular.

Even though it refers to two people, it means each one of the two. Latin treats that idea distributively, one by one, so the verb is singular:

• uterque testis verum dicit = each witness says the truth

If Latin wanted to present them simply as a pair, it could use a plural subject such as ambo testes, and then the verb would be plural:

• ambo testes verum dicunt

Uterque means each of the two or, in many contexts, both.

The important idea is that it is used when there are exactly two people or things under discussion. So it does not mean every in a general sense; it means each one out of two.

That is why English may translate it as both, but Latin still uses singular grammar with it.

Not by itself in this sentence.

Latin does have an enclitic -que meaning and, but in uterque the word is a fixed form meaning each of the two / both. So you should learn uterque as a whole word.

Historically, the -que is related to the same particle, but in normal reading you do not translate uterque as which of two and or anything like that. It simply means each of the two.

Testis is nominative singular.

It is the subject noun, and it agrees with uterque, which is also nominative singular. Together, uterque testis means each witness.

A few useful forms of testis:

• nominative singular: testis
• genitive singular: testis
• nominative plural: testes

It is a third-declension noun.

Because here verum is being used as a substantive adjective, meaning what is true or simply the truth.

It comes from verus, vera, verum meaning true, but the neuter singular often functions like an abstract noun in Latin. So:

• verum dicit = he says what is true / he tells the truth

This is a very common Latin pattern.

Formally, it is an adjective, but in this sentence it is being used like a noun.

That is called a substantive adjective. Latin does this often, especially with neuter singular adjectives.

So verum here is not describing testis. It is the direct object of dicit and means something like:

• the true thing
• what is true
• the truth

Yes. Latin could also say veritatem dicit.

The difference is mainly one of expression:

• verum dicit = says what is true
• veritatem dicit = says the truth

Both are good Latin. In this sentence, verum is just the more compact neuter-adjective way of expressing the idea.

Because Latin has no definite or indefinite article.

So Latin does not have separate words for the or a/an. Whether you understand testis as a witness or the witness depends on context.

That means uterque testis can naturally be understood as each witness or each of the two witnesses, depending on the situation already known from the context.

Yes. Latin word order is more flexible than English word order because the endings show the grammatical roles.

So the following are all possible, though they may sound slightly different in emphasis:

• Uterque testis verum dicit
• Verum uterque testis dicit
• Uterque verum testis dicit

The original order is straightforward and natural. With different orders, Latin may emphasize verum or uterque, but the basic meaning stays the same.

Both can often be translated as both, but they are not quite the same.

• uterque = each of the two, treated individually, so it takes singular grammar
• ambo = both together, treated as a pair, so it takes plural grammar

Compare:

• uterque testis verum dicit = each witness says the truth
• ambo testes verum dicunt = both witnesses say the truth

That is one of the most important things to notice in this sentence.