\Lig"nin\ (l[i^]g"n[i^]n), n. [L. lignum wood: cf. F.
lignine.] (Bot.)
A substance characterizing wood cells and differing from
cellulose in its conduct with certain chemical reagents.
Note: Recent authors have distinguished four forms of this
      substance, naming them lignose, lignin, lignone, and
      lignireose.