Söluaðilinn brosir.

The dictionary form is söluaðili.

In this sentence, söluaðilinn is the definite singular nominative form, meaning the sales agent / the dealer / the salesperson.

So:

• söluaðili = a sales agent / dealer / salesperson
• söluaðilinn = the sales agent / dealer / salesperson

The ending -inn is the definite article, equivalent to English the.

Icelandic usually attaches the to the end of the noun instead of using a separate word before it.

So:

• söluaðili = a sales agent / salesperson
• söluaðilinn = the sales agent / salesperson

This is very common in Icelandic.

Because when the definite article is added to many masculine nouns ending in -i, that final -i drops.

So the pattern is:

• söluaðili
  • -inn → söluaðilinn

This is normal and not something unusual about this word specifically.

Yes, söluaðili is masculine.

That matters because Icelandic nouns have gender, and gender affects:

• the form of the definite article
• adjective agreement
• some case endings

In this sentence, söluaðilinn is masculine singular nominative because it is the subject of the sentence.

Yes. It is a compound:

• sölu- = related to sale / sales
• aðili = party, person, member, participant

So söluaðili literally means something like sales person/party, and in natural English it can mean dealer, vendor, sales agent, or salesperson, depending on context.

Brosir is the present tense of the verb brosa, which means to smile.

Here it is third person singular:

• ég brosi = I smile
• þú brosir = you smile
• hann/hún/það brosir = he/she/it smiles

So in Söluaðilinn brosir, brosir means smiles or is smiling.

It can mean either, depending on context.

Icelandic present tense often covers both:

• smiles
• is smiling

So Söluaðilinn brosir could mean:

• The salesperson smiles
  or
• The salesperson is smiling

English makes this distinction more often than Icelandic does.

Because the subject is already stated: söluaðilinn.

In English, you also would not normally say:

• The salesperson he smiles

You would just say:

• The salesperson smiles

So Icelandic works the same way here: the noun itself is the subject, and no extra pronoun is needed.

No. This is the normal basic word order for a simple statement:

• Söluaðilinn = subject
• brosir = verb

So it follows a basic Subject + Verb pattern:

• Söluaðilinn brosir = The salesperson smiles

That said, Icelandic can change word order more than English in some contexts, especially when another element is placed first:

• Í dag brosir söluaðilinn = Today the salesperson is smiling

But the sentence you were given is the straightforward neutral order.

A rough guide is:

• SÖ-lu-a-thi-linn BRO-sir

A few important sounds:

• ö is like German ö or the vowel in French peur
• ð is like th in this
• Icelandic b is usually pronounced more like an unaspirated p than an English b
• stress normally falls on the first syllable of each word

So the main stress is on:

• SÖluaðilinn
• BROsir

You would normally say:

Söluaðili brosir.

Without the definite ending -inn, the noun is indefinite.

So:

• Söluaðili brosir = A salesperson smiles
• Söluaðilinn brosir = The salesperson smiles

Unlike English, Icelandic often has no separate word corresponding exactly to a/an.