kosteuttavaan
Kosteuttavaan is the illative singular form of the Finnish present active participle kosteuttava, derived from the verb kostuttaa meaning to moisten or hydrate. The form reflects how Finnish participles can function like adjectives and take case endings to agree with the noun they describe.
In usage, kosteuttava describes something that provides moisture or hydration. When it accompanies a noun in
Examples of the illative usage include kosteuttavaan voiteeseen (into a moisturizing cream / toward a moisturizing cream)
Kosteuttavaan is thus part of Finnish morphology where participles behave as adjectives and inflect for case,
See also: kostuttaa, the verb meaning to moisten; present active participles in Finnish; Finnish case system