Source : Webster's Revised Unabridged Dictionary (1913)

Importantly \Im*por"tant*ly\, adv.
   In an important manner.

Source : WordNet®

importantly
     adv 1: in an important way or to an important degree; "more
            importantly, Weber held that the manifold meaning
            attached to the event by the social scientist could
            alter his definition of the concrete event itself"
            [syn: {significantly}]
     2: in an important way; "for centuries jellies have figured
        importantly among English desserts, particularly upon
        festive occasion"