Это небольшая неприятность.

In this sentence, это means this is or it is, not this directly matching the noun.

So Это небольшая неприятность is literally something like:

• This is a small неприятность
• more naturally: It’s a small inconvenience / a minor неприятность

By contrast, эта is the feminine form of this used directly before a feminine noun:

• эта неприятность = this inconvenience

So:

• Это небольшая неприятность. = This is a minor inconvenience.
• Эта неприятность... = This inconvenience...

Неприятность is in the nominative singular.

This is because the sentence is an equational sentence:
Это X = This is X

After это in this kind of sentence, Russian often uses the nominative for the thing being identified.

So:

• неприятность = nominative singular
• dictionary form: неприятность

Because it agrees with неприятность, which is:

• feminine
• singular
• nominative

Russian adjectives must agree with the noun they describe in gender, number, and case.

So:

• masculine: небольшой
• feminine: небольшая
• neuter: небольшое
• plural: небольшие

Since неприятность is feminine, you get:

• небольшая неприятность

A good clue is the ending -ость.

Nouns ending in -ость are very often feminine in Russian:

• новость = news
• скорость = speed
• возможность = possibility
• неприятность = inconvenience / unpleasantness / trouble

Also, feminine nouns in the nominative singular often take adjectives ending in -ая:

• небольшая неприятность

In the present tense, Russian usually omits the verb to be (есть) in simple statements.

So English:

• This is a minor inconvenience.

Russian:

• Это небольшая неприятность.

You usually do not say Это есть небольшая неприятность in normal modern Russian. That sounds unnatural in most everyday contexts.

Both can relate to small, but they are not always identical.

• маленькая usually means physically small, little in size
• небольшая often means small in amount, degree, or importance; minor, not serious

So with неприятность, небольшая is usually more natural, because an inconvenience is not literally “small” in physical size. It means:

• minor inconvenience
• small problem
• nothing too serious

Маленькая неприятность is possible, but небольшая неприятность sounds more idiomatic in many contexts.

Because небольшой is commonly used as a single adjective meaning:

• small
• not large
• minor

Written together, небольшая functions like a normal adjective with its own established meaning.

Compare:

• небольшая неприятность = a minor inconvenience
• не большая, а маленькая... type contrasts can sometimes lead to separate writing, but that is a different structure

In this sentence, the standard form is:

• небольшая

The neutral, standard word order is:

• Это небольшая неприятность.

Russian word order is flexible, but changes in order often affect emphasis or sound less natural.

For example:

• Это небольшая неприятность. = neutral, normal
• Небольшая неприятность — это... = possible if you are defining or contrasting something
• Небольшая неприятность это. = unusual in normal speech

So for a learner, the safest version is:

• Это небольшая неприятность.

Неприятность comes from the idea of something unpleasant and usually means:

• inconvenience
• trouble
• unpleasant incident
• annoyance

Depending on context, Это небольшая неприятность could mean:

• It’s a minor inconvenience.
• It’s a small problem.
• It’s nothing serious.

So the exact English translation depends on the situation.

A useful pronunciation guide is:

• Э́то небольша́я неприя́тность.

Stress:

• Э́то
• небольша́я
• неприя́тность

A rough English-style approximation:

• EH-ta ni-bahl-SHA-ya ni-pri-YAT-nast’

A few notes:

• это is pronounced more like эта in fast speech: [эта]
• the я in небольшая gives a ya sound
• the final ть in неприятность is soft

Sometimes, yes, depending on context.

Literally, it means:

• It’s a minor inconvenience
• It’s a small unpleasantness / small problem

In context, a speaker might use it to reassure someone, which can feel close to:

• It’s no big deal
• It’s nothing serious

But that is a contextual translation, not a word-for-word one.

Russian has no articles like a or the.

So:

• небольшая неприятность can mean a minor inconvenience or the minor inconvenience, depending on context

Russian relies on context, word order, and emphasis instead of articles.

That is why:

• Это небольшая неприятность.

needs no separate word for a.