'postero-superior' originates from New/Modern Latin (medical usage), combining the prefix 'postero-' from Latin 'posterus' meaning 'coming after, behind' and 'superior' from Latin 'superus' meaning 'above'.

'postero-superior' developed as a compound term in medical/New Latin usage from the Latin words 'posterior' and 'superior', and was adopted into anatomical English in this compounded form to specify a combined directional relation.

Initially the Latin elements separately meant 'behind' and 'above'; combined in anatomical terminology they specifically convey the directional phrase 'behind and above' relative to a reference structure, a specialized usage that has remained stable.