'simoniacal' originates from Medieval Latin, specifically the word 'simoniacus' (from 'simonia'), where 'Simoni-' referred to Simon Magus (a personal name associated with the practice) and the suffix '-acus'/'-al' meant 'pertaining to'.

'simoniacus' (Medieval Latin) passed into Late Latin/Old French forms related to 'simony' and then into Middle English as 'simonical' or similar forms, eventually yielding the modern English adjective 'simoniacal'.

Initially it meant 'of or relating to Simon Magus or the practice of simony', and over time it has come to mean more generally 'relating to or characterized by the buying or selling of ecclesiastical offices; corrupt or venal'.