Друг купил безделушку.

Because it is the direct object of the verb купил (bought), so it takes the accusative case.

• Dictionary form: безделушка
• Accusative singular: безделушку

This happens because безделушка is a feminine noun ending in -а. For many feminine nouns like this:

• nominative: -а
• accusative: -у

So:

• безделушка = a trinket / knickknack
• купил безделушку = bought a trinket

Because друг is the subject of the sentence, and subjects normally stand in the nominative case, which is the basic dictionary form.

So here:

• друг = the friend / a friend
• купил = bought
• безделушку = a trinket

The subject is the person doing the action, so друг stays in the nominative.

In Russian past tense, the verb agrees with the subject in gender and number.

• купил = masculine singular
• купила = feminine singular
• купило = neuter singular
• купили = plural

Since друг is a masculine noun, the verb is купил.

So this sentence specifically means that a male friend bought the trinket.

By itself, друг most basically means male friend.

Depending on context, it can sometimes be understood more broadly, and in some situations words for friend can overlap with romantic meanings, but the normal first interpretation is simply friend.

If you wanted to say female friend, you would usually say подруга.

So in this sentence, the most natural reading is:

• Друг купил безделушку. = A/The male friend bought a trinket.

Russian has no articles, so it does not have direct equivalents of English a/an and the.

That means Друг купил безделушку could mean:

• A friend bought a trinket
• The friend bought the trinket
• A friend bought the trinket
• The friend bought a trinket

Which one is intended depends on context.

Russian usually shows this kind of meaning through word order, context, intonation, or previous mention, rather than articles.

Купить / купил is perfective. That means the action is seen as completed.

So Друг купил безделушку means the friend bought the trinket as a completed event.

The imperfective partner is покупать. For example:

• Друг покупал безделушку. = The friend was buying / used to buy a trinket

So the sentence with купил focuses on the fact that the purchase was successfully completed.

Yes. Russian word order is more flexible than English because cases show grammatical roles.

The neutral order here is:

• Друг купил безделушку.

But other orders are possible, for example:

• Безделушку купил друг.
• Купил друг безделушку.

These usually sound different in emphasis or focus, not in core meaning.

For learners, it is best to treat Друг купил безделушку as the most straightforward, neutral version:

• subject + verb + object

Безделушка means something like:

• trinket
• knickknack
• bauble
• small decorative thing
• sometimes something frivolous or unimportant

It often refers to a small object that is not very useful, more decorative or trivial than necessary.

So it is not just any object; it usually suggests something small and somewhat insignificant.

The ending shows it.

• singular nominative: безделушка
• singular accusative: безделушку
• plural nominative: безделушки
• plural accusative: безделушки for inanimate nouns

So безделушку is clearly singular accusative.

Also, the sentence has купил, which is singular masculine past tense, agreeing with друг, not with the object.

The stress is:

• друг
• купи́л
• безделу́шку

So you can say it approximately like:

• drook koo-PEEL beez-deh-LOOSH-koo

A slightly more natural English-style approximation would be:

• drook ku-PEEL byez-dye-LOOSH-ku

A few notes:

• у sounds like oo
• unstressed vowels are often reduced in actual speech
• final consonants can sound less voiced than English learners expect

Because Russian accusative endings depend on both gender and sometimes animacy.

Here, безделушка is:

• feminine
• singular
• inanimate

So it changes from -а to -у in the accusative.

For masculine nouns, things can work differently:

• Я вижу стол. = I see a table
  (стол stays the same because it is masculine inanimate)

• Я вижу друга. = I see a friend
  (друг changes because it is masculine animate)

So Russian object forms are not one-size-fits-all; they depend on noun type.

Yes, in some contexts that is a reasonable English translation.

Russian купил is past tense perfective, which often corresponds to English:

• bought
• has bought

The best English choice depends on context.

So if the emphasis is on a completed result relevant now, English might use:

• The friend has bought a trinket

But if it is just a past event in a story, English might use:

• The friend bought a trinket

The dictionary form is купить.

In dictionaries, Russian verbs are normally listed in the infinitive, so you would look up:

• купить = to buy

From that you get the past masculine singular form:

• купил = bought

So if you want to learn the verb from this sentence, the form to memorize is купить.