Why does Unisex refer to something to do with both sexes, not just one sex?
In the Oxford English Dictionary it says that the word uni means something to do with one of something. How came the word unisex which means something to do with both sexes in the design of clothes and hair? It would make more sense if unisex meant only for one sex: male or female?
The combining form uni- does indeed normally mean one & having or consisting of one coming as it does from Latin unus meaning one. And the Oxford English University contains entries for unisexual and unisexuality which are older than unisex and have the meanings one would expect.
Unisex was coined in the 1960s for use in relatively informal contexts and seems to have been influenced by words such as union, united, universal giving the sense shared rather than single. Thus unisex can be understood as one clothing style/hair salon shared by both sexes.