wichtigem
Wichtigem is a declined form of the German adjective wichtig, meaning important or significant. It is used in the dative case for masculine or neuter singular nouns when the adjective carries the strong declension (i.e., there is no determiner such as ein, der, das). In practice, you will often see it in prepositional phrases such as mit wichtigem Hinweis (with an important hint) or in important abstract phrases such as in wichtigem Maße (to a significant extent). When a determiner is present, other endings appear (for example, dem wichtigen Mann with a definite article uses a different ending).
In the strong declension, the dative singular masculine or neuter ending is -em, producing forms like wichtigem.
Etymology and relation to related forms
The adjective wichtig derives from the noun Wichtung/Wichtigkeit (importance) and has a long history in the
wichti—Wichtigkeit; wichtig; German adjective declension; German grammar.