'postero-inferior' originates from Latin elements: 'postero-' from Latin 'posterus' meaning 'coming after, subsequent, behind', and 'inferior' from Latin 'inferus' meaning 'low' or 'below'.

'posterior' and 'inferior' entered English via Medieval/Latin and Old French usage (Middle English 'posterior', from Latin 'posterior') and (Latin 'inferior' from 'inferus'); the compound form 'postero-inferior' is a modern anatomical/medical compound formed in New/Modern Latin and English by combining these elements.

Initially derived from elements meaning 'behind' and 'below'; in modern anatomical usage it specifically denotes a location that is both posterior and inferior relative to another structure.