"In the 17c., 'protestant' was primarily opposed to 'papist,' and thus accepted by English Churchmen generally; in more recent times, being generally opposed to 'Roman Catholic,' or ... to 'Catholic,' ... it is viewed with disfavour by those who lay stress on the claim of the Anglican Church to be equally Catholic with the Roman." [OED]Often contemptuous shortened form Prot is from 1725, in Irish English. Protestant (work) ethic (1926) is taken from Max Weber's work "Die protestantische Ethik und der 'Geist' des Kapitalismus" (1904).
A Christian belonging to one of the three great divisions of Christianity (the other two are the Roman Catholic Church and the Eastern Orthodox Church). Protestantism began during the Renaissance as a protest against the established (Roman Catholic) church. That protest, led by Martin Luther, was called the Reformation, because it sprang from a desire to reform the church and cleanse it of corruption, such as the selling of indulgences.
Note: Protestants hold a great variety of beliefs, but they are united in rejecting the authority of the pope. Protestant groups include the Amish, the Anglican Communion, the Assemblies of God, the Baptists, Christian Science, the Congregationalists, the Lutheran Church, the Mennonites, the Methodists, the Presbyterian Church, and the Quakers.