The Collaborative International Dictionary of English v.0.48:

Intensive \In*ten"sive\, a. [Cf. F. intensif. See Intense.]
   [1913 Webster]
   1. Stretched; admitting of intension, or increase of degree;
      that can be intensified. --Sir M. Hale.
      [1913 Webster]

   2. Characterized by persistence; intent; unremitted;
      assiduous; intense. [Obs.] --Sir H. Wotton.
      [1913 Webster]

   3. (Gram.) Serving to give force or emphasis; as, an
      intensive verb or preposition.
      [1913 Webster]

   4. (Agric.) Designating, or pertaining to, any system of
      farming or horticulture, usually practiced on small pieces
      of land, in which the soil is thoroughly worked and
      fertilized so as to get as much return as possible; --
      opposed to extensive.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Intensive \In*ten"sive\, n.
   That which intensifies or emphasizes; an intensive verb or
   word.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intensive
    adj 1: characterized by a high degree or intensity; often used
           as a combining form; "the questioning was intensive";
           "intensive care"; "research-intensive"; "a labor-
           intensive industry"
    2: tending to give force or emphasis; "an intensive adverb"
    3: of agriculture; intended to increase productivity of a fixed
       area by expending more capital and labor; "intensive
       agriculture"; "intensive conditions" [ant: extensive]
    n 1: a modifier that has little meaning except to intensify the
         meaning it modifies; "`up' in `finished up' is an
         intensifier"; "`honestly' in `I honestly don't know' is an
         intensifier" [syn: intensifier, intensive]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "intensive":
   absolute, all-embracing, all-encompassing, all-out, all-pervading,
   born, broad-based, clean, clear, comprehensive, concentrated,
   congenital, consummate, deep, deep-dyed, downright,
   dyed-in-the-wool, egregious, exhaustive, hard, intense,
   intensified, omnibus, omnipresent, out-and-out, outright, perfect,
   pervasive, plain, plumb, profound, pure, radical, regular, sheer,
   straight, sweeping, thorough, thoroughgoing, through-and-through,
   total, ubiquitous, unconditional, universal, unmitigated,
   unqualified, unreserved, unrestricted, utter, veritable,
   wholesale