'unfrock' originates from Middle English, specifically the prefix 'un-' meaning 'reverse' and 'frock' meaning 'a priest's robe'.

'unfrock' changed from the Middle English word 'unfroc' and eventually became the modern English word 'unfrock'.

Initially, it meant 'to remove a robe', but over time it evolved into its current meaning of 'to remove a priest from office'.