Kašnjenje je veliki problem.

It is a noun here.

Kašnjenje means delay, lateness, or being late, depending on context. It is formed from the verb kasniti (to be late / to run late), but in this sentence it functions as a regular noun.

So grammatically, the sentence is built like:

Kašnjenje = the subject
je = is
veliki problem = the predicate noun phrase

Je is the 3rd person singular present form of biti (to be).

So:

• ja sam = I am
• ti si = you are
• on/ona/ono je = he/she/it is

In this sentence, je simply means is.

Serbian often uses this short form in normal statements:

• Kašnjenje je problem. = Delay is a problem.

The fuller form jeste also exists, but it is usually used for emphasis or contrast:

• Kašnjenje jeste problem. = Delay really is a problem.

Because je is a clitic in Serbian. Clitics are short unstressed words that usually go in second position in the sentence or clause.

So in a neutral sentence, Serbian naturally says:

Kašnjenje je veliki problem.

not usually:

Je kašnjenje veliki problem.
unless you are asking a question or using a special structure.

This second-position behavior is very common in Serbian and is something English speakers have to get used to.

Because veliki agrees with problem, not with kašnjenje.

In Kašnjenje je veliki problem, the phrase veliki problem means a big problem. The adjective veliki modifies problem, and problem is a masculine singular noun.

So the adjective must also be masculine singular:

• veliki problem = big problem

Even though kašnjenje is neuter, veliki is not describing kašnjenje directly as an adjective before it. It is part of the noun phrase veliki problem.

Both are in the nominative here.

This is because the sentence is an equational sentence with biti (to be):

Kašnjenje je veliki problem.
Literally: Delay is a big problem.

In Serbian, when one noun is identified as another with biti, the complement is normally also in the nominative.

So:

• To je problem.
• Ona je doktorka.
• Kašnjenje je veliki problem.

Because Serbian does not have articles like English a/an/the.

That means Serbian leaves this distinction to context.

So Kašnjenje je veliki problem can naturally be understood as:

• Delay is a big problem
• The delay is a big problem

If you want to make it more specific, Serbian usually adds another word, for example:

• Ovo kašnjenje je veliki problem. = This delay is a big problem.
• To kašnjenje je veliki problem. = That delay is a big problem.

It can mean both, depending on context.

Common meanings include:

• delay
• lateness
• being late

So this sentence could be understood as:

• Delay is a big problem
• Being late is a big problem
• Lateness is a big problem

The exact English translation depends on the situation, but the Serbian sentence itself is completely natural.

Yes, Serbian word order is more flexible than English word order, although some versions sound more neutral than others.

The most neutral version is:

Kašnjenje je veliki problem.

But you could also say:

• Veliki problem je kašnjenje. = The big problem is delay / The big problem is being late.

This version puts more focus on veliki problem.

What usually stays important is the position of the clitic je, which tends to remain in second position in its clause.

Yes, you may hear that too.

Both veliki problem and velik problem exist. For learners, veliki problem is the safest and most standard form to use.

A simple way to think about it is:

• veliki problem = the regular full form
• velik problem = a shorter variant that is also common

If you are unsure, use veliki.

A rough guide is:

kaš-nje-nje

A few useful points:

• š sounds like sh in shoe
• nj sounds like ny in canyon or like Spanish ñ

So kašnjenje has that ny sound twice.

The hardest part for many English speakers is the middle:

• šnje

It helps to say it slowly first:

• kaš-nje-nje

Yes, here it is singular.

It is often used as an abstract noun, like lateness or delay in general. But it can also have a plural:

• kašnjenje = delay / lateness
• kašnjenja = delays

For example:

• Kašnjenja su veliki problem. = Delays are a big problem.

So the noun can refer either to the general idea of delay or to individual delays, depending on context.

Because -nje is a very common noun-forming ending in Serbian.

It often creates nouns that describe:

• an action
• a process
• the result of an action

So from verbs, Serbian often forms nouns like this:

• učiti = to learn
  učenje = learning

• kašniti = to be late
  kašnjenje = being late / delay

This is a useful pattern to recognize, because you will see many nouns ending in -nje while learning Serbian.

Yes. Problem is a masculine noun in Serbian.

Many borrowed international words behave like regular masculine nouns in Serbian:

• problem
• telefon
• hotel
• program

So in nominative singular, they often appear with masculine adjective forms:

• veliki problem
• nov hotel
• dobar program

That is why veliki is masculine here.