Source : Webster's Revised Unabridged Dictionary (1913)

Extensively \Ex*ten"sive*ly\, adv.
   To a great extent; widely; largely; as, a story is
   extensively circulated.

Source : WordNet®

extensively
     adv 1: in a widespread way; "oxidation ponds are extensively used
            for sewage treatment in the Midwest"
     2: to a great extent