'segregatory' originates from Latin, specifically the verb 'segregare,' where 'se-' meant 'apart' and 'gregare' (from 'grex, greg-') meant 'flock' or 'group'.

'segregare' entered Medieval/Late Latin as 'segregatus' and the verb form 'segregate' was later borrowed into English (17th century); the adjective was formed with the suffix '-ory' to produce 'segregatory'.

Initially it meant 'to separate from the flock or group,' but over time it came to be used for actions or measures that separate or divide groups — now often used of policies or practices that enforce separation.