Learn Icelandic: Við keyptum ykkur óvæntan glaðning.

This is a great example of the "dative of advantage" (Dativus commodi). In Icelandic, you frequently skip using a preposition like fyrir (for) when you do an action for someone's benefit. Instead, you just put the beneficiary (in this case ykkur, meaning "for you all") directly into the dative case right after the verb.

Could I say Við keyptum óvæntan glaðning fyrir ykkur instead?

Yes, that is grammatically correct and means exactly the same thing. However, using the dative of advantage (Við keyptum ykkur...) is very common and often sounds more natural and concise in spoken Icelandic, especially with everyday verbs like kaupa (to buy), búa til (to make), or sækja (to fetch).

Why does the adjective óvæntan end in -an?

It is a strong adjective modifying the masculine noun glaðningur (treat). Because the treat is the direct object being bought, it is in the accusative case. The accusative, masculine, singular, strong ending for adjectives is -an, which changes the dictionary form óvæntur into óvæntan.

What is the base form of glaðning, and where does the word come from?