Onsdagen kommer etter tirsdagen.

The ending -en is the definite singular ending. It works a bit like the in English.

• onsdag = Wednesday
• onsdagen = the Wednesday
• tirsdag = Tuesday
• tirsdagen = the Tuesday

So the sentence is literally something like The Wednesday comes after the Tuesday.

That is grammatical, but in a general statement about the order of the weekdays, Norwegian often prefers the basic form without the definite ending:

• Onsdag kommer etter tirsdag.

Not usually. The more natural general statement is:

• Onsdag kommer etter tirsdag.

Using onsdagen and tirsdagen sounds more specific, as if you are talking about particular days in a certain context, not just the general order of the week.

So:

• Onsdag kommer etter tirsdag = the normal generic statement
• Onsdagen kommer etter tirsdagen = understandable, but more marked/specific

In Norwegian, days of the week are normally not capitalized.

So normally you write:

• onsdag
• tirsdag

But the first word of a sentence is capitalized, so:

• Onsdagen kommer etter tirsdagen.

Only Onsdagen has a capital letter because it starts the sentence.

Kommer is the present tense of å komme, which means to come.

Here it is used in the same kind of way English uses comes in sequences:

• Wednesday comes after Tuesday
• Onsdag kommer etter tirsdag

So kommer does not mean physical movement here. It means something like comes next in the order.

Etter means after.

It is a preposition, and here it shows the order of the days:

• etter tirsdag = after Tuesday
• etter tirsdagen = after the Tuesday

So the structure is:

• X kommer etter Y
• X comes after Y

Examples:

• Torsdag kommer etter onsdag.
• Fredag kommer etter torsdag.

Because Norwegian often puts the onto the end of the noun instead of using a separate word.

Compare:

• dag = day
• dagen = the day

So:

• tirsdag = Tuesday
• tirsdagen = the Tuesday

This is very common in Norwegian. English uses a separate word (the), but Norwegian often uses a suffix.

Yes. This is normal Norwegian main-clause word order:

• Onsdagen = subject
• kommer = verb
• etter tirsdagen = prepositional phrase

So the pattern is:

• Subject + verb + rest

That gives:

• Onsdagen kommer etter tirsdagen.

Norwegian main clauses usually follow the verb-second rule, so the finite verb is in the second position.

Yes, absolutely.

• Onsdag kommer etter tirsdag
• Etter tirsdag kommer onsdag

Both are correct.

The second version emphasizes the after Tuesday part a bit more. It is a very natural alternative.

Notice the word order: when Etter tirsdag comes first, the verb still has to stay in second position:

• Etter tirsdag kommer onsdag
• not Etter tirsdag onsdag kommer

The dictionary forms are:

• onsdag
• tirsdag

Those are the forms you would usually look up.

The -en forms are just the definite forms built from them:

• onsdag → onsdagen
• tirsdag → tirsdagen

So if you see a weekday with -en, it is often helpful to mentally strip that ending off to find the base word.

In modern Bokmål, weekday names normally behave like common-gender nouns, so you would use en if you needed an indefinite article:

• en onsdag
• en tirsdag

In practice, with days of the week, Norwegian often uses the noun without an article in many common expressions:

• på tirsdag = on Tuesday
• onsdag kommer etter tirsdag

So while en is the grammatical article, bare forms like onsdag and tirsdag are extremely common.