Learn Dutch: Ik zeg de afspraak af, tenzij de mist verdwijnt. - I am cancelling the appointment, unless the fog disappears.

It is because afzeggen (to cancel) is a separable verb. In a main clause like this one, the core verb (zeg) takes the normal second position, while the prefix (af) gets pushed to the end of that clause.

How does tenzij affect the word order in the second half of the sentence?

Tenzij (unless) is a subordinating conjunction, which means it starts a dependent clause. In Dutch dependent clauses, the conjugated verb is pushed to the very end. Here, verdwijnt is at the end. If you added an extra word like snel (quickly), it would go before the verb: tenzij de mist snel verdwijnt.

The English translation says 'I am cancelling', but I don't see a verb for 'am'. Why?

Dutch doesn't strictly need a separate continuous form (like 'am doing' or 'is happening') to show that an action is ongoing. The simple present tense ik zeg af naturally translates to both 'I cancel' and 'I am cancelling'.

Can afspraak mean something else besides 'appointment'?

Yes! Besides 'appointment', afspraak can also mean an 'agreement' or a 'deal'. However, with the verb afzeggen (to cancel), 'appointment' is the most natural translation here.