'posterior' originates from Latin, specifically the word 'posterior', the comparative of 'posterus', where 'posterus' meant 'coming after' or 'that which follows'.

'posterior' passed from Latin into Late Latin/Medieval Latin and then into Middle English as 'posterior', eventually becoming the modern English 'posterior'.

Initially, it meant 'coming after' or 'subsequent in time or order'; over time it gained the spatial sense 'situated at the back' and later also developed specialized senses such as anatomical 'buttocks' and the statistical sense 'posterior probability'.