1702; plural of humanity (n.), which had been used in English from late 15c. in a sense "class of studies concerned with human culture" (opposed variously and at different times to divinity or sciences). Latin literae humaniores, the "more human studies" (literally "letters") are fondly believed to have been so called because they were those branches of literature (ancient classics, rhetoric, poetry) which tended to humanize or refine by their influence, but the distinction was rather of secular topics as opposed to divine ones (literae divinae).
From the late Middle Ages, the singular word humanity served to distinguish classical studies from natural sciences on one side and sacred studies (divinity) on the other side. ... The term's modern career is not well charted. But by the eighteenth century humanity in its academic sense seems to have fallen out of widespread use, except in Scottish universities (where it meant the study of Latin). Its revival as a plural in the course of the following century apparently arose from a need for a label for the multiple new 'liberal studies' or 'culture studies' entering university curricula. [James Turner, "Philology," 2014]