Methylene

n.
  1. A divalent 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.
    2. Methylene blue (Chem.),
    an artificial dyestuff consisting of a complex sulphur derivative of diphenyl amine; -- called also pure blue.