Source : Webster's Revised Unabridged Dictionary (1913)

Methylene \Meth"yl*ene\, n. [F. m['e]thyl[`e]ne, from Gr. ? wine
   + ? wood; -- a word coined to correspond to the name wood
   spirit.] (Chem.)
   A hydrocarbon radical, {CH2}, not known in the free state,
   but regarded as an essential residue and component of certain
   derivatives of methane; as, methylene bromide, {CH2Br2}; --
   formerly called also {methene}.

   {Methylene blue} (Chem.), an artificial dyestuff consisting
      of a complex sulphur derivative of diphenyl amine; --
      called also {pure blue}.

Source : WordNet®

methylene blue
     n : a dark green dye used as a stain, an antiseptic, a chemical
         indicator, and an antidote in cyanide poisoning [syn: {methylthionine
         chloride}]