Synonyms for Extensive:

adj.

across-the-board (adjective)
global.
all (adjective)
extended.
far-flung (adjective)
wide-reaching.
far-reaching (adjective)
far-ranging, far-reaching.
far-reaching, thorough (adjective)
long, wide-ranging, general, huge, great, unrestricted, sweeping, sizable, spacious, vast, roomy, considerable, boundless, capacious, big, voluminous, broad, inclusive, comprehensive, wide, large-scale, widespread, extended, large.
inclusive (adjective)
comprehensive.
large (adjective)
gigantic, awesome, magnificent, cavernous, bulky, majestic, copious, baggy, vast, massive, great, capacious, immense, roomy, generous, impressive, humongous, prodigious, colossal, sizable, grand, elephantine, lofty, mammoth, princely, ample, huge, voluminous, tremendous, grandiose, gargantuan, towering, big, enormous, large, soaring, comprehensive, giant, expansive, spacious.
long (adjective)
linear, stretched, long, lengthwise, endwise, reaching, elongated.
size (adjective)
portly, sizable, long, big, great, corpulent, measurable, wide, magnificent, high, chunky, dimensional, voluminous, broad, amplitudinous, large, bulky, expansive.
wide-ranging (adjective)
sweeping.

n.

widely, substantial. king-size, healthy, large-scale, good, tidy. global, blow-by-blow, overall, edited, broad-spectrum, general, elaborate, inclusive, wide-ranging, descriptive, wide-reaching, specific, all-round, 101, detailed, far-ranging, widespread, all-around, broad-brush. comprehensive (noun)
thorough, inclusive.
extensive (noun)
copious, big, abundant, considerable, voluminous, extended, wide, comprehensive, far-reaching, large, sweeping.
widespread (noun)
general, unrestricted, widespread, boundless.

Other synonyms:

detailed, all-round, widely, wide-ranging, general, edited, descriptive, blow-by-blow, broad-brush, far-ranging, substantial, large-scale, specific, broad-spectrum, all-around, wide-reaching, overall. inclusive, global. widespread. tidy, healthy. good. detailed
elaborate.

Usage examples for extensive

  1. There is a very extensive literature upon this subject. – The Teaching of Geometry by David Eugene Smith