Vinnudagurinn minn byrjar snemma á mánudögum.

Icelandic very often builds compound nouns, just like English does in words such as workday or weekday.

So vinnudagurinn can be broken down like this:

• vinnu- = work
• dagur = day
• -inn / -urinn = the

So vinnudagurinn means the workday.

In this sentence it is the subject, and its full form is nominative singular masculine.

That is a very common Icelandic pattern.

Icelandic often uses:

• definite noun + possessive

where English usually uses:

• possessive + noun

So:

• vinnudagurinn minn = literally something like the workday mine
• natural English = my workday

This is normal Icelandic, not extra emphasis. You will see the same pattern in phrases like:

• bíllinn minn = my car
• bókin mín = my book
• húsið mitt = my house

Because that is the usual position for a possessive pronoun when the noun is definite in Icelandic.

So Icelandic prefers:

• vinnudagurinn minn

rather than trying to mirror English word order.

Also, minn changes form to match the noun it belongs to. Here it is minn because vinnudagur is:

• masculine
• singular
• nominative

If the noun were feminine or neuter, or in another case, the possessive would change form too.

Byrjar is the present tense form of the verb að byrja = to begin / to start.

The subject is vinnudagurinn minn, which is third person singular, so the verb must match that.

A few present-tense forms of að byrja are:

• ég byrja = I begin
• þú byrjar = you begin
• hann / hún / það byrjar = he / she / it begins

Since vinnudagurinn minn is a singular subject, Icelandic uses byrjar.

Snemma is an adverb, and here it means early.

It describes how or when the workday starts:

• byrjar snemma = starts early

Unlike nouns, adjectives, and possessive pronouns, an adverb like snemma does not change for gender, number, or case.

Because á mánudögum means on Mondays in the sense of a repeated, habitual action.

So:

• á mánudögum = on Mondays, every Monday, on Mondays in general
• á mánudag = on Monday, one specific Monday

In this sentence, the speaker is talking about a routine, so the plural form makes sense:

• Vinnudagurinn minn byrjar snemma á mánudögum.
• My workday starts early on Mondays.

Mánudögum is dative plural.

This is a very useful time-expression pattern to learn as a chunk:

• á mánudag = on Monday
• á mánudögum = on Mondays

Yes, it is a good idea to memorize weekday expressions this way, because prepositions in Icelandic often affect case, and the forms do not always match what an English speaker might expect.

So for practical learning, it is often best to remember the whole phrase rather than only the dictionary form.

The basic word order here is very natural:

• Vinnudagurinn minn byrjar snemma á mánudögum.

But Icelandic word order is somewhat flexible. In a main clause, the finite verb usually stays in second position.

For example, you could also say:

• Á mánudögum byrjar vinnudagurinn minn snemma.

That is also correct and natural.

But you cannot just move words freely in any order. Icelandic follows a verb-second pattern much more strongly than English.

Because in Icelandic, the names of the days of the week are normally written with a lowercase letter.

So:

• mánudagur = Monday
• þriðjudagur = Tuesday
• miðvikudagur = Wednesday

This is different from English, where Monday is capitalized. In Icelandic, you only capitalize it if it comes at the beginning of a sentence.

The dictionary forms are:

• vinnudagur = workday
• mánudagur = Monday

What you see in the sentence are inflected forms:

• vinnudagurinn = vinnudagur in the definite nominative singular
• mánudögum = mánudagur in the dative plural

This is very typical of Icelandic: the form in the sentence is often not the same as the dictionary form, because Icelandic marks case, number, gender, and definiteness directly on words.