This is the 842nd most frequent Icelandic word.
milljörðum
"Milljörðum" means "billions" (dative plural) in English.
The word "milljörðum" is related to "milljarða" used here in the dative plural form as it indicates an action directed at "billion" entities in Icelandic.
Hann gaf tvo milljarða til góðgerðamála.
He donated two billion to charity.
"Milljörðum" is used in this sentence in dative plural form to describe the quantity 'in billions'.
Þeir töluðu um fjármagn sem nam milljörðum króna.
They talked about funds amounting to billions of krona.
Here, "milljörðum" is again in the dative plural and functions to specify the scope of savings as 'billions'.