The term was coined in the 1960s and was used fairly informally. Though the combining form 'uni-' is from the Latin 'unus' meaning 'one', the term seems to have been influenced by words such as 'united' and 'universal', meaning that the 'uni-' prefix takes on the definition of 'shared'. In this sense, it can be seen as meaning 'shared by both sexes'.
Hair stylists and beauty salons that serve both men and women are often referred to as unisex. This is typical of other services that traditionally separated the sexes, such as clothing shops.