SINGLE-CATEGORY . of Latin monkey, one, unique, solo and catenary, string. The catenary is the curve that forms a chain or rope when hung from its ends at the same height, as happens between the cable laying poles. It is used to differentiate viruses that have a traditional DNA with the double helix of nucleotides, called bicatenary, from those that have only one chain, as is the case in RNA, and in which case they are defined, according to the Baltimore standard, as single-stranded