Termosflasken holder varmen, om så bare en stund.

Because -en is the definite singular ending.

• en termosflaske = a thermos flask / a vacuum bottle
• termosflasken = the thermos flask

Norwegian often attaches the definite article to the end of the noun instead of using a separate word like English the.

Also, termosflaske is a compound noun:

• termos = thermos
• flaske = bottle

So termosflasken literally means the thermos bottle.

Holder is the present tense of å holde.

• å holde = to hold / keep
• holder = holds / keeps

So:

• Termosflasken holder varmen = The thermos keeps the heat / The thermos keeps things warm

Norwegian verbs do not change for person the way English verbs sometimes do. So the same present-tense form is used with all subjects:

• jeg holder
• du holder
• den holder

Because Norwegian often uses the definite form in expressions like this.

• varme = heat / warmth
• varmen = the heat / the warmth

In holde varmen, the definite form is natural and idiomatic. It does not necessarily mean one specific, sharply defined heat in the English sense. It is just how Norwegian commonly phrases this idea.

So holde varmen means something like:

• keep the heat in
• retain warmth
• keep warm

This is one of those places where Norwegian structure does not match English word-for-word.

Here it means to retain heat or to keep something warm.

With a thermos, the idea is that the thermos keeps the contents warm by holding in the heat.

So the phrase is not about physically holding heat with your hands. It is more like:

• The thermos retains the heat
• The thermos keeps the warmth in

The same expression can also be used about people:

• Prøv å holde varmen. = Try to keep warm.

So the phrase is flexible, but here it is being used about the thermos’s function.

Om så bare is an idiomatic expression meaning something like:

• even if only
• if only
• even if just

So:

• om så bare en stund = if only for a while / even if only for a little while

It is not best understood by translating each word too literally, but the parts are roughly:

• om = if / even if
• så = so, here adding emphasis
• bare = only / just

Together, they create a concessive idea: even if the amount of time is small, it still counts.

Yes, ei stund is also possible.

Stund is traditionally a feminine noun, so in Bokmål you may see:

• ei stund = a while

But Bokmål often allows many feminine nouns to take common-gender forms too, so you can also say:

• en stund

Both are normal in Bokmål. A learner will often see en stund in standard written Norwegian, even though ei stund is also correct.

Here, en stund simply means for a while or for some time, usually a limited or not very long time.

Bare means only or just.

It limits en stund:

• en stund = a while
• bare en stund = only a while / just a while

So the sentence suggests that the thermos keeps the heat, but perhaps not for very long. It adds a slightly modest or restrained tone:

• It keeps the heat — even if only for a while.

The comma marks a pause before an added comment or afterthought.

The main clause is:

• Termosflasken holder varmen

Then om så bare en stund is added as a kind of qualifying remark:

• ..., if only for a while

So the comma helps show that the second part is not the main statement, but an extra nuance.

In practice, this gives the sentence a slightly literary or reflective rhythm.

Not really in the usual sense. It is more of an elliptical expression.

A fuller paraphrase could be something like:

• om det så bare er en stund

That would mean:

• even if it is only for a while

In the original sentence, some words are left out because the shorter version is natural and elegant. Norwegian often allows this kind of compression in idiomatic expressions.

It sounds a bit more polished or literary than the most basic everyday phrasing.

A very plain version might be something like:

• Termosflasken holder drikken varm en stund.

But:

• Termosflasken holder varmen, om så bare en stund.

has a more reflective tone. It feels slightly expressive, as if the speaker is acknowledging a limitation: it does keep the heat, even if only temporarily.

So the sentence is perfectly natural, but it is a little more stylistically shaped than the most straightforward everyday wording.