Learn Danish: Er billetten tur-retur? - Is the ticket a return?

The base word is en billet (a ticket). When we add the definite ending -en to make it 'the ticket', the final consonant is doubled to keep the vowel sound short. So, billet becomes billetten.

What does tur-retur literally translate to?

It literally means 'trip-return'. In Danish, this is the standard way to say 'round-trip' or 'return' when talking about tickets for trains, buses, or flights. If you only want a one-way ticket, you would ask for an enkeltbillet.

Why don't we say en tur-retur like we say 'a return' in English?

In English, 'a return' is a noun. In this Danish sentence, tur-retur acts more like an adjective describing the ticket. You are literally asking 'Is the ticket round-trip?' so no extra article like en is needed.

Why does the sentence start with the verb Er?

Just like in English, Danish forms yes/no questions by swapping the subject and the verb. The statement 'The ticket is a return' would be Billetten er tur-retur. To ask it as a question, you flip the subject (billetten) and the verb (er) to get Er billetten tur-retur?.