aktiivsel
Aktiivsel is an inflected form of the Estonian adjective aktiivne, meaning "active." It is the singular adessive case form (adessive suffix -l attached to the genitive stem), used to mark location, presence, possession in constructions like "X-l on Y," and certain adverbial or instrumental relations.
Morphology and pronunciation: the base adjective aktiivne (genitive aktiivse) takes the adessive ending -l to yield
Syntactic role and usage: aktiivsel typically appears together with a noun in the adessive case and agrees
Relation to other forms: aktiivsel contrasts with the nominative aktiivne, genitive aktiivse, and partitive aktiivset; plural