Source : Webster's Revised Unabridged Dictionary (1913)

   {Yeast cake}, a mealy cake impregnated with the live germs of
      the yeast plant, and used as a conveniently transportable
      substitute for yeast.

   {Yeast plant} (Bot.), the vegetable organism, or fungus, of
      which beer yeast consists. The yeast plant is composed of
      simple cells, or granules, about one three-thousandth of
      an inch in diameter, often united into filaments which
      reproduce by budding, and under certain circumstances by
      the formation of spores. The name is extended to other
      ferments of the same genus. See {Saccharomyces}.

   {Yeast powder}, a baling powder, -- used instead of yeast in
      leavening bread.