Sui generis
In sociology, the "sui generis" is what has been externalized, then internalized in the overall public and becomes a part of society that simply exists in its construct. It is not something that is not thought to have been created, because it is imbedded in everyone's way of thinking and being. Instances include the idea of love, or going to school, or clothing belonging to a specific gender. These examples are "sui generis" for they simply exist in society and are widely accepted without thoughts of where they come from or how they were created.
Gender
The modern English word "gender" comes from the Middle English "gender", "gendre", a loanword from Anglo-Norman and Middle French "gendre". This, in turn, came from Latin "genus". Both words mean "kind", "type", or "sort". They derive ultimately from a widely attested Proto-Indo-European (PIE) root "gn-",
which is also the source of "kin", "kind", "king", and many other English words. It appears in Modern French in the word "genre" (type, kind, also "") and is related to the Greek root "gen-" (to produce), appearing in "gene", "genesis", and "oxygen". The Oxford Etymological Dictionary of the English Language of 1882 defined "gender" as "kind, breed, sex", derived from the Latin ablative case of "genus", like "genere natus", which refers to birth. The first edition of the Oxford English Dictionary (OED1, Volume 4, 1900) notes the original meaning of "gender" as "kind" had already become obsolete.