'Protestantism' originates from 'Protestant', which comes from the Latin word 'protestari', where 'pro-' meant 'publicly' and 'testari' meant 'to bear witness'. The suffix '-ism' denotes a system or practice.

'Protestantism' developed from the word 'Protestant', which was first used in the 16th century to describe those who protested against certain practices of the Roman Catholic Church, and eventually became the term for the religious movement and its beliefs.

Initially, it referred specifically to the beliefs and practices of those who protested against the Catholic Church, but over time it evolved to mean the entire branch of Christianity distinct from Catholicism and Orthodoxy.