This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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ad. In an extensive manner, widely.

ad. To a great extent.

ad. To a great extent; widely; largely.

With regard to extension or extent.

In an extensive manner; widely; largely; to a great extent: as, a story extensively circulated.

ad. in a widespread way

"Ludwig Feuerbach uses the term extensively in a criti - cal sense, coupled with “empiricism” and “positivism,” to denote historical relativism and the uncritical acceptance of the world as it presents itself."

widely    largely   

comprehensively    defensively    expensively    inexpensively    intensively