Miles amicum in periculo non deserit.

Because amicum is the accusative singular form of amicus (friend). In this sentence, the friend is the direct object of deserit (abandons / deserts), so Latin puts amicus into the accusative case.

• amicus = a friend
• amicum = a friend (as the object)

English mostly shows this by word order, but Latin often shows it by word ending.

Here miles does happen to come first, but even if it did not, it would still be the subject because of its form and its relationship to the verb.

Miles is nominative singular, so it means the soldier as the subject of the action. Latin relies much more on case endings than English does. English usually needs subject–verb–object order to make roles clear, but Latin can often change the order without changing the basic meaning.

So in this sentence:

• miles = subject
• amicum = direct object
• deserit = verb

Because Latin often expresses this idea with the prepositional phrase in periculo, literally in danger or in peril.

• in = in
• periculo = danger / peril, in the ablative singular

This is a very normal Latin way to express a state or situation. English also uses a preposition here, so this part is fairly close to English.

Because the preposition in takes the ablative when it means in, on, or in a state/situation of without motion.

Here there is no movement into danger; the meaning is that the friend is already in danger. So Latin uses:

• in + ablative = in / in a state of
• in periculo = in danger

Compare that with a different use:

• in + accusative often shows motion into something

So in periculum would suggest into danger, not simply in danger.

Deserit is present tense, third person singular, active voice.

It comes from desero, deserere = to abandon, to desert.

The ending -it tells you:

• third person = he/she/it
• singular = one subject
• present = abandons / is abandoning

So miles ... non deserit means the soldier does not abandon...

Because non normally negates the word or phrase that follows, and very often it comes directly before the verb.

So:

• non deserit = does not abandon

This is the most straightforward and common placement. Latin word order is flexible, but placing non before the verb is very natural.

Yes, often they could. Because Latin uses endings to show grammatical roles, the order can be changed for emphasis.

For example, these would still basically mean the same thing:

• Miles amicum in periculo non deserit.
• Amicum miles in periculo non deserit.
• In periculo amicum miles non deserit.

The core meaning stays the same because:

• miles is still nominative
• amicum is still accusative
• periculo is still ablative after in
• deserit is still the verb

However, different word orders can shift emphasis or style.

It can mean either, depending on context.

Latin has no definite or indefinite article, so miles can mean:

• the soldier
• a soldier

Likewise, amicum can mean:

• the friend
• a friend

The wider context usually tells you which is more natural in translation.

Because Latin verb endings already include the subject information.

Deserit means he/she/it abandons, so a separate pronoun is usually unnecessary unless Latin wants to add emphasis or contrast.

So instead of saying something like he does not abandon, Latin can simply say:

• non deserit

And if the subject noun is already there, as in miles, that is enough.

Not by itself. Amicum just means friend in the accusative singular. Latin has not explicitly said his friend here.

Depending on context, English might translate it as his friend, because that sounds natural, but the Latin sentence itself only states a/the friend.

If Latin wanted to be more explicit, it could add a possessive word such as suum:

• amicum suum = his own friend

The dictionary forms are:

• miles from miles, militis = soldier
• amicum from amicus, amici = friend
• in = in
• periculo from periculum, periculi = danger, peril
• non = not
• deserit from desero, deserere, deserui, desertum = abandon, desert

This is useful because Latin words often appear in sentences in forms that differ from the dictionary form.

Because that is how natural English works. Latin can negate a finite verb simply by putting non before it:

• non deserit = literally something like not abandons

But in correct English, present tense negation usually needs do/does:

• does not abandon

So this is not extra meaning in Latin; it is just the normal way to express the same idea in English.

Yes. Miles is a third-declension noun, even though an English speaker might expect a masculine noun naming a person to look more like a second-declension noun such as amicus.

Its forms are different:

• nominative singular: miles
• genitive singular: militis

So learners often need to remember that miles belongs to a different declension from amicus, even though both refer to male persons here.