Six, spelled out (as opposed to "6"), often appears in the names of the older Japanese 6×6 folders or rigid cameras. Most of them were inspired by the Zeiss Ikon Ikonta and Nettar 6×6 models. Apparently the Super Ikonta B was sold in Japan under the name Super Six; maybe it is the origin of the designation.
In Japanese script, it is written シックス; conventionally romanized, the term is shikkusu.
"Six" was to some extent superseded by "66"; the two terms sometimes appear together ("Mine Six Super 66").