Andstæðingurinn brosir.

In Icelandic, the definite article is usually added to the end of the noun instead of written as a separate word.

So here:

• andstæðingur = opponent
• andstæðingurinn = the opponent

That ending -inn / -urinn is the attached definite article. This is one of the first big differences English speakers notice, because Icelandic usually does not use a separate word like English the.

Andstæðingurinn is:

• masculine
• singular
• nominative
• definite

It is in the nominative case because it is the subject of the sentence.

The basic dictionary form is andstæðingur. In this sentence, that noun has been changed into its definite nominative singular form: andstæðingurinn.

The dictionary form is andstæðingur.

That is the form you would usually look up in a dictionary. Icelandic dictionaries normally list nouns in the indefinite nominative singular.

So:

• dictionary form: andstæðingur
• form used here: andstæðingurinn

Brosir is the present tense form of the verb að brosa.

In this sentence, it is 3rd person singular present because the subject is andstæðingurinn.

A useful mini-conjugation is:

• ég brosi = I smile
• þú brosir = you smile
• hann/hún/það brosir = he/she/it smiles
• við brosum = we smile
• þið brosið = you all smile
• þeir/þær/þau brosa = they smile

So here, brosir matches a singular subject.

Yes. By itself, brosir can be either:

• you smile with þú
• he/she/it smiles with a 3rd person singular subject

For example:

• Þú brosir. = You smile.
• Andstæðingurinn brosir. = The opponent smiles / is smiling.

So the subject tells you which meaning is intended.

It can mean either one, depending on context.

Icelandic often uses the simple present where English might use either:

• smiles
• is smiling

So Andstæðingurinn brosir can naturally correspond to either of these in English.

If Icelandic wants to be more explicitly progressive, it can use a structure like:

• Andstæðingurinn er að brosa.

But in many ordinary situations, the simple present brosir is enough.

Because Icelandic finite verbs do not agree with the subject in gender. They mainly agree in person and number.

So you get:

• andstæðingurinn brosir = masculine subject
• konan brosir = feminine subject
• barnið brosir = neuter subject

The verb stays brosir in all three cases because the subject is still 3rd person singular.

This is the normal, neutral word order for a simple statement:

• subject + verb
• Andstæðingurinn brosir.

But Icelandic word order can change, especially because Icelandic is a verb-second language.

For example:

• Núna brosir andstæðingurinn. = Now the opponent is smiling.

And if you turn it into a yes/no question, the verb comes first:

• Brosir andstæðingurinn? = Is the opponent smiling?

So the sentence as written is the standard statement form.

A few helpful pronunciation points:

• Icelandic words are usually stressed on the first syllable
• æ is roughly like the vowel in eye
• ð is roughly like th in this
• brosir is stressed on bro-

So the main stresses are on:

• ANdstæðingurinn
• BROsir

For an English speaker, the hardest parts are usually the æ and ð in andstæðingurinn, plus getting used to the Icelandic rhythm. Audio is very helpful here, because Icelandic spelling is fairly regular once you learn the sound rules.

Grammatically, andstæðingur is the indefinite form of the noun, so removing the definite ending changes the opponent to an indefinite or more general opponent.

However, bare singular nouns in Icelandic do not always line up perfectly with English a/an in every context, so the exact feel depends on the sentence and situation.

The key contrast you should learn from this example is:

• andstæðingur = indefinite base form
• andstæðingurinn = definite form

So the sentence you were given is specifically using the definite noun form.