Sui generis
A similar case that led to the use of the label "sui generis" is the relationship of New Caledonia relative to France, because the legal status of New Caledonia can aptly be said to lie somewhere between a French overseas collectivity and a sovereign nation. Although other examples of such status for other dependent or disputed territories may exist, this arrangement is unique within the French realm.
Sincerity
According to the American Heritage Dictionary, the Latin word "sincerus" is derived from the Indo-European root "*sm̥kēros", itself derived from the zero-grade of "*sem" ("one") and the suffixed, lengthened e-grade of "*ker" ("grow"), generating the underlying meaning "of one growth", hence "pure, clean."