1. Relating to the group of atoms derived from methane containing one carbon atom and two hydrogen atoms.
2. A hydrocarbon radical not known in the free state, but regarded as an essential residue and component of certain derivatives of methane; such as, methylene bromide, formerly called methene.
3. Methylene blue, an artificial dyestuff consisting of a complex sulphur derivative of diphenyl amine.
4. Originally: a hydrocarbon radical present in wood spirit (which consists chiefly of methanol).