Haltu í handriðið þegar þú ferð niður stigann.

Haltu is the singular imperative of að halda. It means hold! or, in this sentence, hold on to ... when speaking to one person.

So:

• að halda = to hold / keep
• haltu = hold! (said to one person)
• haldið = hold! (said to more than one person)

In Icelandic, commands usually do not need the subject pronoun. The imperative form already shows that you are speaking to you.

So Haltu í handriðið is the normal way to say Hold the handrail / Hold on to the handrail.

You can add þú for emphasis in some contexts, but it is usually unnecessary.

Because halda í is a very common expression meaning hold on to or grip something.

That is slightly different from bare halda, which can have other meanings such as keep, maintain, hold in a more general sense.

So here:

• halda í handriðið = hold on to the handrail

It is best to learn halda í as a set expression.

Yes, í often means in/into, but with some verbs it becomes part of a fixed expression. Here, halda í means hold on to.

So you should not translate it too literally as hold in the handrail. Instead, treat halda í + accusative as the natural Icelandic pattern for hold on to something.

The -ið is the suffixed definite article, so handriðið means the handrail.

The base noun is:

• handrið = handrail

With the definite article:

• handriðið = the handrail

Icelandic usually adds the to the end of the noun instead of using a separate word like English does.

It is accusative singular definite.

That is because halda í normally takes the accusative. This is something learners usually need to memorize as part of the expression.

A useful point here is that for this neuter noun, the accusative singular looks the same as the nominative singular:

• handrið = a handrail
• handriðið = the handrail

So the form itself does not visibly change much, but grammatically it is accusative here.

Þegar means when here. It introduces a time clause:

• þegar þú ferð niður stigann = when you go down the stairs

So the whole sentence means something like:

• Hold on to the handrail when you go down the stairs.

Because the verb is að fara (to go), and ferð is the correct 2nd person singular present form:

• ég fer = I go
• þú ferð = you go
• hann/hún/það fer = he/she/it goes

So þú ferð means you go.

Because after a subordinating word like þegar, Icelandic normally uses subordinate clause word order, where the subject comes before the finite verb:

• þegar þú ferð ... = when you go ...

In a main clause, Icelandic often has verb-second word order, but subordinate clauses are different. So þegar þú ferð is the normal structure here.

Here niður means down, and stigann means the stairs / the staircase in the accusative singular.

This construction expresses movement along a route:

• fara niður stigann = go down the stairs

So stigann is not just sitting there randomly; it tells you what route is being gone down.

Because Icelandic often uses the singular noun stigi for what English commonly calls stairs.

So:

• stigi = stairs / staircase / stairway
• stigann = the stairs / the staircase

English prefers a plural word here, but Icelandic often uses the singular. That is completely normal.

The basic form is stigi, which is a masculine noun.

Here are the relevant forms:

• stigi = a staircase / stairs
• stiginn = the staircase / the stairs
• stigann = the staircase / the stairs (accusative)

In this sentence, stigann is used because the phrase describes movement down the stairs.

It is addressed to one person.

You can tell because of:

• haltu = singular imperative
• þú ferð = singular you go

If you were speaking to more than one person, the forms would be different.