Við grínumst saman.

Here it means we.

Icelandic has two different words spelled við:

• við = we (pronoun)
• við = a preposition that can mean things like with, by, against, depending on context

In Við grínumst saman, Við is the subject, so it means we.

The dictionary form is grínast, which means to joke, to kid around, or sometimes to be joking.

So:

• grínast = to joke
• grínumst = we joke / we are joking

This is the normal verb form; you do not start from a separate plain verb like grína in this meaning.

Because grínumst is the 1st person plural present tense form of the verb grínast.

A very useful way to see it is:

• ég grínast = I joke
• þú grínast = you joke
• við grínumst = we joke
• þið grínist = you all joke

The -st is part of the verb itself, and -um marks we. Together they give -umst.

This kind of verb is often called a middle-voice or -st verb. In many cases, English does not translate that -st separately; it is just part of how the Icelandic verb works.

Not really.

Even though -st historically relates to reflexive meaning in some verbs, in a sentence like Við grínumst saman, it does not literally mean we joke ourselves.

Instead, grínast is just the normal Icelandic verb for to joke / kid around. So you should learn grínast as a whole verb.

You do not need an extra word like okkur here.

Saman means together.

So the sentence very literally is:

• Við = we
• grínumst = joke / are joking
• saman = together

It adds the idea that the joking is shared or mutual: we joke together.

You can often say just Við grínumst, and it is still grammatical. Adding saman simply makes the together/with each other idea more explicit.

It can mean either one, depending on context.

Icelandic present tense often covers both:

• simple present: we joke together
• present progressive: we are joking together

So Við grínumst saman could describe:

• a general habit: We joke together a lot
• something happening now: We’re joking together

Context tells you which meaning is intended.

Yes, absolutely.

• Við grínumst saman = neutral present; can mean we joke together or we are joking together
• Við erum að grínast saman = more explicitly we are joking together right now

The vera að + infinitive construction often highlights an action in progress.

So both are correct, but Við erum að grínast saman feels more clearly ongoing at this moment.

Usually it suggests joking, kidding around, or being playful. It is often friendly.

Depending on tone and context, it can sometimes come close to teasing, but if you specifically mean making fun of someone, Icelandic often uses other expressions, especially:

• gera grín að einhverjum = to make fun of someone
• stríða einhverjum = to tease someone

So Við grínumst saman normally sounds like we joke around together, not necessarily we mock each other.

Yes, but Icelandic has rules about it.

The basic statement order here is:

• Við grínumst saman.

If you move another element to the front, the verb usually stays in second position:

• Oft grínumst við saman. = We often joke together.

In a yes/no question, the verb comes first:

• Grínumst við saman? = Are we joking together? / Do we joke together?

So the sentence you were given is the normal straightforward statement, but other word orders are possible depending on emphasis or sentence type.