The Collaborative International Dictionary of English v.0.48:

Chromatin \Chro"ma*tin\, n. (Biol.)
   The deeply staining substance of the nucleus and chromosomes
   of eukaryotic cells, composed of DNA and basic proteins (such
   as histones), the DNA of which comprises the predominant
   physical basis of inheritance. It was, at the beginning of
   the 20th century, supposed to be the same substance as was
   then termed idioplasm or germ plasm. In most eukaryotic
   cells, there is also DNA in certain plasmids, such as
   mitochondria, or (in plant cells) chloroplasts; but with the
   exception of these cytoplasmic genetic factors, the nuclear
   DNA of the chromatin is believed to contain all the genetic
   information required to code for the development of an adult
   organism. In the interphase nucleus the chromosomes are
   dispersed, but during cell division or meiosis they are
   condensed into the individually recognizable chromosomes. The
   set of chromosomes, or a photographic representation of the
   full set of chromosomes of a cell (often ordered for
   presentation) is called a karyotype.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Chromatin \Chro"ma*tin\, n. [Gr. ?, ?, color.]
   1. (Biol.) Tissue which is capable of being stained by dyes.
      [archaic]
      [1913 Webster]

WordNet (r) 3.0 (2006):

chromatin
    n 1: the readily stainable substance of a cell nucleus
         consisting of DNA and RNA and various proteins; during
         mitotic division it condenses into chromosomes [syn:
         chromatin, chromatin granule]