December is koud.

Yes. In Dutch, month names are normally written with a lowercase letter: december, januari, maart, and so on.

It is capitalized here only because it is the first word of the sentence:

• December is koud.

If the month appeared later in the sentence, you would usually write:

• In december is het koud.

Because December is the name of a month, and month names are treated like proper names in this kind of sentence. Dutch does not use an article here, just like English:

• December is koud.
• Januari is lang.

You normally would not say de december or een december in this meaning.

Is is the third-person singular present tense of zijn (to be).

The subject is December, which is singular, so Dutch uses is:

• December is koud.
• De maand is koud.

This works very much like English December is cold.

Because koud comes after the verb is and is being used as a predicate adjective. In Dutch, adjectives after zijn usually stay in the basic form:

• December is koud.
• Het water is koud.

You often get -e only when the adjective comes before a noun:

• de koude maand
• een koude winter

So:

• December is koud. ✅
• de koude decembermaand ✅
• December is koude. ❌

It is grammatical and understandable, but it can sound a bit general, literary, or simplified.

In everyday Dutch, people are often more likely to say:

• In december is het koud. = In December it is cold.
• December is een koude maand. = December is a cold month.

So December is koud is not wrong, but it is a bit less common than those alternatives.

The sentence follows the basic Dutch main-clause order:

subject + finite verb + complement

So here:

• December = subject
• is = finite verb
• koud = adjective/complement

This is the same basic pattern as in English:

• December is cold.

Yes. Koud can describe physical temperature, but it can also be used figuratively, depending on context.

Examples:

• Het is koud. = The weather is cold.
• Haar handen zijn koud. = Her hands are cold.
• Een koude reactie. = A cold reaction.

In December is koud, the most obvious meaning is about weather or climate.

A rough English-friendly guide is:

• December ≈ day-SEM-bur
• is ≈ iss
• koud ≈ something like kowt (rhyming roughly with out, but with a Dutch sound)

A few useful notes:

• The eu sound does not appear in december; the stress is on -cem-.
• ou in koud is a Dutch diphthong, somewhat like the vowel in English house.
• The final d in koud is often pronounced more like a t sound in normal speech.

Yes, absolutely. That is a very natural sentence.

Compare:

• December is koud.
• In december is het koud.
• Het is koud in december.

All are understandable, but the last two often sound more idiomatic in everyday Dutch when talking about weather.

Literally, December is the month. But in a sentence like December is koud, Dutch speakers understand that you mean the month of December is cold or December is a cold time.

So the sentence is really using the month name to talk about the typical weather or climate associated with that month. English does the same thing:

• December is cold.

Yes. The same pattern works with other months:

• Januari is koud.
• Februari is kort.
• Augustus is warm.

Just remember that month names are normally lowercase unless they begin the sentence:

• Januari is koud.
• In januari is het koud.