Questions & Answers about Hún borðar ein í kvöld.
Ein agrees with Hún (she).
- Hún is feminine, singular, nominative.
- The word einn/ein/eitt inflects like an adjective and must agree with the subject when it means “alone”:
- masculine nominative singular: einn
- feminine nominative singular: ein
- neuter nominative singular: eitt
So with hún, you must say ein.
Eina is the accusative feminine form and would be used for a direct object, e.g.:
In Hún borðar ein í kvöld, ein is not an object; it’s a predicate word meaning alone that describes hún, so it stays in the nominative feminine: ein.