Лгать другу — позор.

Russian usually omits the present-tense form of to be.

So:

• Лгать другу — позор.
• literally: To lie to a friend — [is] a disgrace.

In English, you need is, but in Russian, in the present tense, it is normally left out.

Compare:

• Он студент. = He is a student.
• Это проблема. = This is a problem.
• Лгать другу — позор. = Lying to a friend is shameful / a disgrace.

If you were speaking about the past or future, forms of быть could appear.

The dash often appears in Russian when one noun phrase or infinitive phrase is being equated with another, especially when the verb is is omitted.

Here it marks the relationship:

• Лгать другу = the action
• позор = what that action is being called

So the dash helps signal:

• Lying to a friend — [is] a disgrace.

It is especially common in short, strong, aphoristic, proverb-like statements.

Without the dash, the sentence would feel less standard in writing. The dash gives it a firm, emphatic, almost moral judgment.

Yes. In Russian, an infinitive can function much like English to lie or lying when talking about an action in general.

So лгать другу means something like:

• to lie to a friend
• lying to a friend

This whole infinitive phrase acts as the subject of the sentence.

Russian does this very naturally:

• Курить вредно. = Smoking is harmful.
• Опаздывать плохо. = Being late is bad.
• Лгать другу — позор. = Lying to a friend is a disgrace.

So this is a normal structure.

Because the verb лгать takes the dative case for the person you lie to.

• друг = nominative
• другу = dative singular

So:

• лгать другу = to lie to a friend
• not to lie a friend

This is just the standard government pattern of the verb.

More examples:

• лгать матери = to lie to one’s mother
• лгать учителю = to lie to the teacher
• лгать детям = to lie to children

A learner often wants to map this directly to English prepositions, but in Russian it is better to remember:

• лгать + dative

By itself, другу just means to a friend or to the friend, depending on context. Russian has no articles, so it does not mark a/the the way English does.

It also does not automatically mean my friend.

So depending on context, this sentence could be understood as:

• Lying to a friend is a disgrace
• Lying to one’s friend is a disgrace
• Lying to your friend is a disgrace

Russian leaves that more open unless something is added, for example:

• лгать своему другу = to lie to one’s own friend / to your friend
• лгать моему другу = to lie to my friend

Позор is a noun meaning:

• disgrace
• shame
• dishonor

In this sentence, it is being used as a strong moral label: the action is being called a disgrace.

So the tone is stronger than simply saying:

• Это плохо. = This is bad.

It is more like:

• This is shameful.
• This is disgraceful.
• This is a disgrace.

Russian often uses nouns this way for forceful judgments:

• Это позор. = This is a disgrace.
• Так поступать — позор. = To act like that is disgraceful / a disgrace.

Both are possible in Russian, but they are slightly different structures.

In your sentence:

• Лгать другу — позор.
• literally: To lie to a friend is a disgrace.

Here позор is a noun.

Another possible sentence:

• Лгать другу позорно.
• It is shameful to lie to a friend.

Here позорно is a predicative adverb/state word, meaning shameful.

So the difference is roughly:

• позор = a disgrace
• позорно = shameful

The version with позор sounds more forceful and slogan-like.

It is natural, but it has a compressed, emphatic, moralizing style.

It sounds like:

• a proverb
• a slogan
• a moral judgment
• a line from a speech or essay

In ordinary conversation, people might more often say:

• Лгать другу стыдно. = It’s shameful to lie to a friend.
• Нельзя лгать другу. = You mustn’t lie to a friend.
• Врать другу плохо. = Lying to a friend is bad.

So Лгать другу — позор is natural, but stylistically strong and concise.

Yes, you could say:

• Врать другу — позор.

That would also be understandable and natural.

The difference is mainly one of style and nuance:

• лгать is a bit more neutral, bookish, or formal
• врать is more colloquial and common in everyday speech

Both mean to lie.

So:

• лгать другу — позор sounds a little more elevated or moralistic
• врать другу — позор sounds more conversational but still strong

For a short aphoristic sentence like this, лгать works especially well.

Лгать is imperfective.

That makes sense because the sentence is talking about the action in general, not one completed instance.

Russian typically uses the imperfective in statements about general behavior, habits, or abstract actions:

• Курить вредно. = Smoking is harmful.
• Обманывать людей плохо. = Deceiving people is bad.
• Лгать другу — позор. = Lying to a friend is a disgrace.

A perfective verb would not fit as well here, because perfective usually points to a single completed act.

A related perfective verb might be солгать or соврать, but those would not normally be used in this kind of general moral statement.

Yes, but the original order is the most straightforward for this meaning.

Original:

• Лгать другу — позор.

This presents:

1. the action first
2. the judgment second

That is very natural for X is Y.

You could also see:

• Позор — лгать другу.

But that sounds more marked, rhetorical, or poetic. It puts heavy emphasis on позор first.

So for a learner, the safest default is:

• [action in infinitive] — [judgment]

The stress is:

• лгать — one syllable, so the stress is there by default
• дрУгу
• позОр

So:

• лгать дрУгу — позОр

A rough pronunciation guide:

• лгать ≈ lgat’
• другу ≈ DROO-goo
• позор ≈ pa-ZOR

A useful thing to notice is that лгать begins with a consonant cluster that may feel awkward at first for English speakers. Listen carefully to native pronunciation and practice it slowly.

Yes. With лгать + dative, it means to lie to someone.

So:

• лгать другу = to lie to a friend

If you wanted to say to lie about a friend, you would need a different structure, for example:

• лгать о друге = to lie about a friend
  though more idiomatic Russian might use another verb depending on context

So the case matters a lot:

• другу = to a friend
• о друге = about a friend

Yes. Even though the Russian literally uses the noun позор = a disgrace, a smoother English translation can be:

• It is shameful to lie to a friend.

That translation captures the moral force well.

So there are two good ways to understand it in English:

• more literal: Lying to a friend is a disgrace.
• more natural in some contexts: It is shameful to lie to a friend.

Both reflect the same basic meaning.