The Collaborative International Dictionary of English v.0.48:

Litharge \Lith"arge\ (l[i^]th"[.a]rj), n. [OE. litarge, F.
   litharge, L. lithargyrus, Gr. liqa`rgyros the scum or foam of
   silver; li`qos stone + 'a`rgyros silver. Litharge is found in
   silverbearing lead ore.] (Chem.)
   Lead monoxide; a yellowish red substance, obtained as an
   amorphous powder, or crystallized in fine scales, by heating
   lead moderately in a current of air or by calcining lead
   nitrate or carbonate. It is used in making flint glass, in
   glazing earthenware, in making red lead or minium, etc.
   Called also massicot.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

massicot \mas"si*cot\, n. [F. massicot; E. masticot is a
   corruption.] (Chem.)
   Lead monoxide (also called Lead protoxide), PbO, obtained
   as a yellow amorphous powder, the fused and crystalline form
   of which is called litharge; lead ocher. It is used as a
   pigment. It is also called lead oxide yellow, as opposed to
   red lead, which is lead tetroxide Pb3O4.
   [1913 Webster +PJC]

   Note: Massicot is sometimes used by painters, and also as a
         drier in the composition of ointments and plasters.
         [1913 Webster]

WordNet (r) 3.0 (2006):

massicot
    n 1: the mineral form of lead monoxide; in the form of yellow
         powder it is used as a pigment [syn: massicot,
         massicotite]