one who protests; -- originally applied to those who adhered to luther, and protested against, or made a solemn declaration of dissent from, a decree of the emperor charles v. and the diet of spires, in 1529, against the reformers, and appealed to a general council; -- now used in a popular sense to designate any christian who does not belong to the roman catholic or the greek church.-making a protest; protesting.-of or pertaining to the faith and practice of those christians who reject the authority of the roman catholic church; as, protestant writers.