Ovaj bol je strašan.

Because bol is a masculine singular noun in the nominative case, and ovaj has to agree with it.

• ovaj = masculine singular
• ova = feminine singular
• ovo = neuter singular

So:

• ovaj bol = this pain
• not ova bol
• not ovo bol

This kind of agreement is very important in Serbian: demonstratives and adjectives change form to match the noun.

Yes, bol is masculine in Serbian.

Grammatical gender in Serbian does not have to match any natural or logical idea. A word can be masculine, feminine, or neuter simply because that is how it behaves grammatically.

You can tell bol is masculine because:

• it ends in a consonant
• adjectives with it take masculine forms: ovaj bol, strašan bol

So even though pain is an abstract idea, the noun bol is grammatically masculine.

For the same reason as ovaj: it must agree with bol.

Since bol is masculine singular nominative, the adjective also has to be masculine singular nominative:

• masculine: strašan
• feminine: strašna
• neuter: strašno

So:

• ovaj bol je strašan
• ova rana je strašna
• ovo iskustvo je strašno

Agreement is one of the core features of Serbian grammar.

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

So:

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

In Ovaj bol je strašan, je links the subject ovaj bol with the description strašan, just like is in English.

Normally, no in this kind of sentence.

In the present tense, Serbian often uses the verb biti explicitly in standard sentences like this:

• Ovaj bol je strašan.

Leaving out je would sound incomplete or nonstandard here.

So for learners, the safe rule is: when saying X is Y, keep je.

Serbian does not have articles like the or a/an.

So Serbian does not mark definiteness the same way English does. Instead, it often relies on:

• context
• word order
• demonstratives like ovaj (this), taj (that), onaj (that over there)

In this sentence, ovaj specifically means this, not just the. If you said only:

• Bol je strašan.

that would mean something like The pain is terrible or Pain is terrible, depending on context.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Ovaj bol je strašan.

But you could also hear:

• Strašan je ovaj bol.
• Ovaj je bol strašan. (more marked, more contrastive)

These versions change the emphasis rather than the basic meaning.

For a learner, Ovaj bol je strašan is the safest and most natural basic version.

A simple English-friendly guide would be:

• stra as in strah without the h
• š sounds like sh
• so strašan is roughly STRAH-shan

A few key points:

• š = sh
• the final n is clearly pronounced
• Serbian spelling is very phonetic, so words are usually pronounced close to how they are written

So strašan sounds approximately like STRA-shan, with a clear sh sound in the middle.

In this sentence, yes.

Here strašan clearly means something like:

• terrible
• awful
• dreadful

But in colloquial Serbian, strašan can sometimes be used more loosely for emphasis, even in a positive sense, a bit like amazing or incredible in casual English.

Still, with bol (pain), it is definitely negative: this pain is terrible.

Because bol is the subject of the sentence.

In Ovaj bol je strašan:

• ovaj bol = the thing being talked about
• je strašan = what is being said about it

Subjects are normally in the nominative in Serbian.

That is why you get:

• ovaj bol
  not, for example, accusative or genitive forms.

Yes, that is very natural too, but it means something slightly different.

• Ovaj bol je strašan. = This pain is terrible.
• Ovaj bol me ubija. = This pain is killing me.

The first sentence is a direct description using to be + adjective. The second is a more vivid, stronger way to talk about the pain.

So the sentence you have is a straightforward descriptive pattern, which is very useful to learn.

The plural of bol is bolovi.

So:

• Ovi bolovi su strašni.

Notice that everything changes to plural:

• ovaj → ovi
• bol → bolovi
• je → su
• strašan → strašni

This is a good example of how Serbian words agree with each other across the whole sentence.