The Collaborative International Dictionary of English v.0.48:

Intrinsic \In*trin"sic\ ([i^]n*tr[i^]n"s[i^]k), a. [L.
   intrinsecus inward, on the inside; intra within + secus
   otherwise, beside; akin to E. second: cf. F. intrins[`e]que.
   See Inter-, Second, and cf. Extrinsic.]
   [1913 Webster]
   1. Inward; internal; hence, true; genuine; real; essential;
      inherent; not merely apparent or accidental; -- opposed to
      extrinsic; as, the intrinsic value of gold or silver;
      the intrinsic merit of an action; the intrinsic worth or
      goodness of a person.
      [1913 Webster]

            He was better qualified than they to estimate justly
            the intrinsic value of Grecian philosophy and
            refinement.                           --I. Taylor.
      [1913 Webster]

   2. (Anat.) Included wholly within an organ or limb, as
      certain groups of muscles; -- opposed to extrinsic.
      [1913 Webster]

   Intrinsic energy of a body (Physics), the work it can do in
      virtue of its actual condition, without any supply of
      energy from without.

   Intrinsic equation of a curve (Geom.), the equation which
      expresses the relation which the length of a curve,
      measured from a given point of it, to a movable point, has
      to the angle which the tangent to the curve at the movable
      point makes with a fixed line.

   Intrinsic value. See the Note under Value, n.

   Syn: Inherent; innate; natural; real; genuine.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Intrinsic \In*trin"sic\, n.
   A genuine quality. [Obs.] --Warburton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intrinsic
    adj 1: belonging to a thing by its very nature; "form was
           treated as something intrinsic, as the very essence of
           the thing"- John Dewey [syn: intrinsic, intrinsical]
           [ant: extrinsic]
    2: situated within or belonging solely to the organ or body part
       on which it acts; "intrinsic muscles"

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "intrinsic":
   actual, appropriate, basic, central, characteristic, congenital,
   connate, constitutional, deep, deep-seated, distinctive,
   distinguished, elemental, esoteric, essential, fundamental,
   genuine, hereditary, idiocratic, idiosyncratic, immanent,
   implanted, implicit, in character, inalienable, inborn, inbred,
   indoor, indwelling, infixed, ingrained, inherent, inherited,
   inmost, innate, inner, innermost, inside, interior, internal,
   intestine, intimate, inward, inwrought, irreducible, marked,
   native, natural, organic, peculiar, private, proper,
   quintessential, real, resident, secret, single, singular,
   subjective, true, true to form, unalienable, unchallengeable,
   underlying, unique, unquestionable