|WikiProject Chemistry||(Rated Stub-class, Low-importance)|
The article says: It is sometimes used non-systematically for a carbon with four single bonds, where one bond is to a hydrogen.
I dispute this. I think most chemist use methine to mean four single bonds where only one bond is to hydrogen.
Methanetriyl group >CH−
The ChEBI database  lists the term "methine" as a synonym for the molecular group formally defined by the IUPAC as "methanylylidene", but not as a synonym for the very common usage of "methine" for the "methanetriyl group >CH− ". The IUPAC of course follows very strict rules of nomenclature, but the latter definition (as observed anonymously previously on this page) is used very frequently and it is found in most organic chemistry texts. I naively thought of the methine group only as a carbon with four single bonds, one a hydrogen. Apparently I was wrong, but to me the formal definition leaves the term ambiguous and leads to confusion in journal articles where the author's vernacular may be different, which accounts for my current snooping. I could not find a better IUPAC reference. Tachyon 03:04, 6 March 2015 (UTC)
-  The Chemical Entities of Biological Interest (ChEBI) database. Accessed on 2015-03-05.