To a large degree; covering a wide area or range; in great detail over a broad scope.
From 'extensive' plus '-ly', where 'extensive' comes from Late Latin 'extensivus', derived from Latin 'extensus' (stretched out), past participle of 'extendere'. The Latin combines 'ex-' (out) with 'tendere' (to stretch), literally meaning 'stretched outward'.
The word 'extensively' beautifully preserves its physical origins - when we study something extensively, we're metaphorically stretching our investigation outward across a broad territory. This spatial metaphor helps explain why 'extensively' implies both breadth and thoroughness, unlike 'intensively' which suggests depth and concentration.
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