'antisexist' originates from modern English, formed by the prefix 'anti-' (meaning 'against') combined with 'sexist' (a person supporting or practicing 'sexism').

'sexist' was coined in the mid-20th century from 'sexism' (the -ist suffix marking an agent), and speakers later formed 'anti-' + 'sexist' to indicate opposition; this produced the modern compound 'antisexist' (also written 'anti-sexist').

Initially it simply combined 'anti-' and 'sexist' to mean 'against a sexist or sexism'; over time it has been used both as an adjective describing attitudes or policies and as a noun for people who oppose sexism.