Mendacium amicitiae nocet, et parva quoque iniuria diu manere potest.

Amicitiae is dative singular, from amicitia, amicitiae (friendship).

It is in the dative because the verb nocere means to harm and normally takes a dative object in Latin. So:

• mendacium = the subject, a lie
• amicitiae = to friendship
• nocet = harms

So literally the structure is A lie harms friendship.

Mendacium is a neuter singular noun meaning lie or falsehood.

Here it is in the nominative singular because it is the subject of nocet:

• mendacium nocet = a lie harms

Its nominative and accusative singular forms look the same because it is a second-declension neuter noun.

Because nocere is one of those Latin verbs that regularly takes the dative, not the accusative.

So Latin says:

• alicui nocere = to harm someone/something

Examples:

• puero nocet = it harms the boy
• rei publicae nocet = it harms the state
• amicitiae nocet = it harms friendship

This is a very common thing English speakers have to get used to, because English uses a direct object here, but Latin does not.

Quoque usually means also, too, or sometimes even.

It often comes after the word it emphasizes. So in:

• parva quoque iniuria

the sense is something like:

• even a small injury
• a small injury too

Latin often places quoque after the emphasized word instead of before it, which can feel unusual to an English speaker.

Iniuria is nominative singular feminine.

It is the subject of potest (and of the infinitive phrase manere with potest):

• parva quoque iniuria ... potest = even a small injury can ...

So the basic structure is:

• iniuria potest manere = an injury/wrong can remain

Depending on context, iniuria can mean injury, wrong, offense, or injustice.

Parva is an adjective meaning small.

It is feminine nominative singular because it agrees with iniuria, which is also feminine nominative singular.

So:

• parva iniuria = a small injury/wrong

This is normal Latin adjective agreement: adjectives agree with their nouns in gender, number, and case.

Potest means is able or can, and manere is a present active infinitive meaning to remain.

Latin commonly uses possum + infinitive:

• potest manere = can remain

So:

• iniuria manere potest = an injury can remain

This is the same idea as English can + verb, except Latin uses a finite verb plus an infinitive.

Diu is an adverb meaning for a long time or long.

It modifies manere:

• diu manere = to remain for a long time

So the second clause means that the injury or offense may last a long time.

Because its subject is singular:

• parva quoque iniuria = even a small injury

Since iniuria is singular, the verb is singular too:

• potest = can

If the subject were plural, you would expect possunt instead.

Latin word order is much more flexible than English word order because Latin uses case endings to show grammatical relationships.

So in this sentence, Latin can say:

• Mendacium amicitiae nocet
• Amicitiae mendacium nocet
• Mendacium nocet amicitiae

and the grammar is still clear because:

• mendacium is nominative
• amicitiae is dative

The chosen order often reflects emphasis, rhythm, or style more than strict grammatical necessity.

Et simply means and, and it joins the two clauses:

• Mendacium amicitiae nocet
• et parva quoque iniuria diu manere potest

So the sentence contains two coordinated statements:

1. A lie harms friendship
2. Even a small injury/offense can last a long time

Yes.

• Mendacium is specifically a lie or falsehood
• Iniuria is broader: injury, wrong, offense, insult, or injustice

So the sentence moves from one specific harmful act, lying, to a more general idea that even a small wrong can have lasting effects.

That nuance helps explain why the second half does not simply repeat the first half in different words.