The term “Protestant” … requires comment. It derives from the aftermath of the Second Diet of Speyer (February 1529), which voted to end the toleration of Lutheranism in Germany. In April of the same year, six German princes and 14 cities protested against this oppressive measure, defending freedom of conscience and the rights of religious minorities. The term “Protestant” derives from this protest.
It is therefore not strictly correct to apply the term “Protestant” to individuals prior to April 1529 or to speak of events prior to that date as constituting “the Protestant Reformation.” The term “evangelical” is often used in the literature to refer to the reforming factions at Wittenberg and elsewhere (e.g., in France and Switzerland) prior to this date. Although the word “Protestant” is often used to refer to this earlier period, this use is, strictly speaking, an anachronism.
McGrath, Alister E.. Reformation Thought: An Introduction (p. 6). Wiley. Kindle Edition.