'readmission' originates from Latin elements: the prefix 're-' from Latin meaning 'again' and 'admission' from Latin 'admissio', where 'ad-' meant 'to/toward' and 'mittere' meant 'to send'.

'admissio' (Latin) passed into Old French as 'admission' and into Middle English as 'admyssioun/admission'; the modern compound 'readmission' formed by adding the Latin prefix 're-' to 'admission' in English.

Initially it meant 'the act of admitting in or allowing entry' and, with the prefix 're-', 'admitting again'; over time the sense has remained similar but has specialized in contexts such as institutional membership and medical readmission.