The Collaborative International Dictionary of English v.0.48:

Glycogen \Gly"co*gen\, n. [Gr. ? sweet + -gen: cf. F.
   glycog[`e]ne.] (Physiol. Chem.)
   A white, amorphous, tasteless substance resembling starch,
   soluble in water to an opalescent fluid. It is found
   abundantly in the liver of most animals, and in small
   quantity in other organs and tissues, particularly in the
   embryo. It is quickly changed into sugar when boiled with
   dilute sulphuric or hydrochloric acid, and also by the action
   of amylolytic ferments.
   [1913 Webster]

WordNet (r) 3.0 (2006):

glycogen
    n 1: one form in which body fuel is stored; stored primarily in
         the liver and broken down into glucose when needed by the
         body [syn: glycogen, animal starch]