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 aktiivsel. In IPA it is approximately /ˈaktiːvsel/; stress falls on the first syllable as in standard Estonian.

Syntactic role and usage: aktiivsel typically appears together with a noun in the adessive case and agrees with that noun in case. Common uses include indicating location ("aktiivsel rühmal oli koosolek" — "the active group had a meeting"), possession or existence ("aktiivsel inimesel on palju kohustusi" — "an active person has many obligations"), and contexts where English would use adverbial phrases ("aktiivsel osalemisel õpid rohkem" — "by participating actively you learn more").

Relation to other forms: aktiivsel contrasts with the nominative aktiivne, genitive aktiivse, and partitive aktiivset; plural adessive is aktiivsetel. The formation mirrors that of many Estonian adjectives, reflecting regular case inflection patterns rather than being a separate lexical item.