Mendacium amicitiam in odium vertit.

The subject is mendacium.

It is a neuter singular nominative noun here, meaning the thing that performs the action. A native English speaker may notice that mendacium could also look accusative, because in many neuter nouns the nominative and accusative have the same form. In this sentence, though, it is understood as the subject from the overall structure and meaning.

Amicitiam is accusative singular.

It is the direct object of vertit. In other words, it is the thing being acted upon: the lie turns friendship into something else.

The basic idea is:

• mendacium = subject
• amicitiam = direct object
• vertit = turns

Because it follows in in a phrase of change into.

Latin often uses this pattern:

aliquid in aliquid vertere
= to turn something into something

So here:

• amicitiam = the thing being changed
• in odium = what it is changed into

With in + accusative, Latin can express movement toward something or change into a new state.

Not in the English sense of location.

Here in means into.

That is a very common point for learners:

• in + ablative usually means in/on = location
• in + accusative usually means into/onto = motion or change toward

Since odium is accusative, in odium means into hatred, not in hatred.

Vertit is from verto, vertere, meaning to turn.

In form, vertit can be either:

• present tense: he/she/it turns
• perfect tense: he/she/it turned

That is normal in Latin: some present and perfect forms look identical.

So by form alone, vertit is ambiguous. Context tells you whether to read it as turns or turned. If your exercise gives the meaning as present, then you should take it here as turns.

Because Latin word order is much more flexible than English word order.

Latin uses word endings much more than position to show grammatical function, so the verb often comes at or near the end of the sentence. That is a very common Latin style.

This order:

Mendacium amicitiam in odium vertit

lets the sentence build naturally:

• the cause: mendacium
• the thing affected: amicitiam
• the result: in odium
• the action: vertit

English depends more on position; Latin often uses position for emphasis or style.

Because Latin has no articles.

So:

• mendacium can mean a lie, the lie, or sometimes simply lying/falsehood
• amicitiam can mean friendship or the friendship
• odium can mean hatred or the hatred

English has to choose an article, but Latin usually leaves that to context.

Yes. It is a very common way to express changing one thing into another.

A useful pattern to remember is:

X Y in Z vertit
= X turns Y into Z

So in this sentence:

• mendacium = what causes the change
• amicitiam = what is changed
• in odium = what it becomes

This is a good pattern to learn as a whole, not just word by word.

Mendacium is a second-declension neuter noun.

That matters mainly because neuter nouns have a special feature:

• nominative singular and accusative singular are the same
• nominative plural and accusative plural are also the same

So a learner may wonder whether mendacium is subject or object. The answer comes from syntax and meaning, not from the ending alone.

In this sentence, it is the subject.