In organic chemistry, a methine group or methine bridge is a trivalent functional group , derived formally from methane. It consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen. The group is also called methyne  or methene, but its IUPAC systematic name is methylylidene or methanylylidene.
This group is sometimes called "methylidyne", however that name belongs properly to either the methylidyne group  (connected to the rest of the molecule by a triple bond) or to the methylidyne radical  (the two atoms as a free molecule with dangling bonds).
The name "methine" is also widely used in non-systematic nomenclature for the methanetriyl group (IUPAC): a carbon atom with four single bonds, where one bond is to a hydrogen atom ().