'defrock' originates from a combination of Latin and Middle English elements: the Latin prefix 'de-' and Middle English 'frok(e)', where 'de-' meant 'off/away' and 'frok(e)' meant 'frock' or 'garment'.

'defrock' was formed in early modern English (first attested in the 17th century) from the prefix 'de-' + Middle English 'frok(e)'; the term developed from the literal idea of removing a frock (garment) to its figurative use of removing clerical status.

Initially it could be understood literally as 'to strip of a frock (garment)', but over time it evolved to mean specifically 'to remove someone from clerical office' (to deprive of ecclesiastical status).