Greinarnar á trénu hreyfast í vindinum, en blómin í beðinu standa kyrr.

The main dictionary forms are:

• grein = branch
• tré = tree
• hreyfast = move
• vindur = wind
• en = but
• blóm = flower
• beð = bed, flowerbed
• standa = stand
• kyrr = still, motionless

It is useful to learn nouns with gender too:

• grein is feminine
• tré is neuter
• blóm is neuter
• beð is neuter
• vindur is masculine

Because Icelandic usually puts the definite article the at the end of the noun.

Here is the buildup:

• grein = branch
• greinar = branches
• greinarnar = the branches

So -nar here is part of the definite plural ending for this feminine noun.

This is a very common question because neuter nouns can look tricky.

For blóm:

• blóm = flower
• blóm can also be flowers in the indefinite plural
• blómið = the flower
• blómin = the flowers

So in this sentence, blómin is definitely plural: the flowers.

Because those nouns come after prepositions and are in the dative case here.

• á trénu = on the tree
• í beðinu = in the bed / flowerbed
• í vindinum = in the wind

The reason is that á and í take the dative when they describe a location rather than movement toward somewhere.

So:

• tré → trénu
• beð → beðinu
• vindur → vindinum

All three also include the definite article, so they mean the tree, the bed, the wind in dative form.

Very roughly:

• á = on, on top of, at
• í = in, inside

So:

• á trénu = on the tree
• í beðinu = in the flowerbed
• í vindinum = in the wind

Both á and í can take either accusative or dative:

• dative for location
• accusative for movement toward

For example:

• í beðinu = in the flowerbed
• í beðið = into the flowerbed

That location vs. direction contrast is very important in Icelandic.

Because hreyfast means to move in the sense of move oneself / be moving, while hreyfa usually means to move something.

Compare:

• Ég hreyfi stólinn. = I move the chair.
• Stóllinn hreyfist. = The chair moves.

So in this sentence, the branches are not moving something else; they themselves are moving. That is why hreyfast is the natural verb.

Also, hreyfast here is the present tense, 3rd person plural, agreeing with greinarnar.

Because the subject is plural: blómin = the flowers.

With standa:

• hann stendur = he stands
• þau standa = they stand

So:

• blómin standa = the flowers stand

This can be confusing because standa is also the infinitive form. In other words, the infinitive and the present plural happen to look the same here.

Kyrr means still, motionless, or without moving.

In standa kyrr, the whole expression means stand still.

Learners often expect an agreeing adjective here, but kyrr is commonly used in a fixed predicative/adverbial way in this expression, so you simply learn:

• standa kyrr = stand still

In this sentence, they most naturally describe the nouns:

• Greinarnar á trénu = the branches on the tree
• blómin í beðinu = the flowers in the flowerbed

So they tell you which branches and which flowers we are talking about.

Then the verbs say what those things do:

• the branches move in the wind
• the flowers stand still

Because Icelandic usually uses a suffixed definite article instead of a separate word like English the.

So English says:

• the branches
• the tree
• the flowers
• the bed
• the wind

But Icelandic builds that into the noun forms:

• greinarnar
• trénu
• blómin
• beðinu
• vindinum

This is one of the biggest structural differences from English.

It has two main clauses joined by en = but:

• Greinarnar á trénu hreyfast í vindinum
• en blómin í beðinu standa kyrr

So the pattern is:

• subject
  • verb
    • other information
• but
• subject
  • verb
    • other information

More literally:

• The branches on the tree move in the wind
• but the flowers in the bed stand still

It is a very natural example of how Icelandic uses noun endings, prepositions, and verb agreement together.