What is the Standard Definition of a Protestant Church?

Question

Note: this is a different question from this one, which posits one definition and asks if it is OK. My question asks for a standard definition. I also hope to know the authorities involved in putting forth such a definition. (I have edited the headline question to include the word "Standard".)

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Is there a standard definition of a Protestant Church? This question came up as a result of my using the guideline in the tag for Protestantism:

Protestantism is a broad tradition referring to the churches which broke from the Roman Catholic Church during the 16th Century and those that descended from them.

The problem with this description is that "those that descended" from the mainline Protestant movement include a number of groups that do not affirm the Nicene Creed. Some reject all or parts of it, while others simply do not demand that members adhere to it. So how should Protestantism be defined if it does not include the various churches that descended from the original Reformation churches of the 16th century?

Here are some short attempts to clarify what the term "Protestant" means.

Wikepedia

Various experts on the subject tried to determine what makes a Christian denomination a part of Protestantism. A common consensus approved by most of them is that if a Christian denomination is to be considered Protestant, it must acknowledge the following three fundamental principles of Protestantism. (Sola Scriptura, Sola Fides and the priesthood of all believers).

Britannica

In England in the early 17th century, the word was used to denote “orthodox” Protestants as opposed to those who were regarded by Anglicans as unorthodox, such as the Baptists or the Quakers. Roman Catholics, however, used it for all who claimed to be Christian but opposed Catholicism (except the Eastern churches). They therefore included Baptists, Quakers, and Catholic-minded Anglicans under the term. Before the year 1700 this broad usage was accepted, though the word was not yet applied to Unitarians.

New World Encyclopedia

Protestants generally may be divided among four basic groups: 1) The "mainline" churches with direct roots in the Protestant reformers, 2) the Radical Reform movement emphasizing adult baptism, 3) nontrinitarian churches, and 4) the Restorationist movements of the late eighteenth and nineteenth centuries. Various denominations exist within each group, and not every denomination fits neatly into these categories.

Learn Religions Website

Protestant churches today consist of hundreds, perhaps even thousands, of denominations with roots in the Reformation movement. While specific denominations vary widely in practice and beliefs, a common doctrinal groundwork exists among them. These churches all reject the ideas of apostolic succession and papal authority.

Summary: None of these definitions addresses the theological boundaries of Protestantism in terms of the Trinity, or other aspects of the Nicene Creed. One specifically includes non-trinitarian traditions. So the question remains: is there a standard definition of what constitutes a Protestant Church? If so, on what authority was this standard decided?

Answer 1

Knowing the historic origins of the name "Protestant" serves to show how far removed most professing Protestants now are from their starting-point. It's interesting to note how few people today who say they are Protestants know any details. (I have not done an academic study into that, but if anyone knows of a source giving such info, I'd be delighted to see it!)

It was first in 1529, at the Second Diet of Speyer, that events conspired to label a new group of non-Catholics as 'Protestants'. It was their objecting to undemocratic religious prejudice regarding the reaffirmation of the Edict of Worms that got them labelled.

They did not give themselves that name but the label stuck, yet became much misunderstood by those unacquainted with the circumstances as to what, precisely, those Christians were protesting about.

The Edict of Worms was reaffirmed only for Catholic territories. Provisionally, and prior to reaffirmation of the Edict of Worms by the general council, Lutheranism was to be tolerated in those regions where it could not be suppressed without tumult. By then, most of northern Germany had become Lutheran, and in the south the cities of Strassburg, Augsburg, Ulm, and Nurnberg. Constance embraced the reform, severed connections with the Hapsburgs, and joined the Swiss. Basel came over to the reform in 1529, the year of the Second Diet of Speyer. Between June 25th to August 27th 1526, the Diet of Speyer deferred action on the Edict of Worms. Here I quote:

"In Lutheran lands, the principle of religious liberty for Catholics must be observed, whereas in Catholic lands the same liberty would not be extended to the Lutherans. Against this invidious arrangement the Evangelicals protested, whence the origin of the name Protestants. They contended that the majority of one diet could not rescind the unanimous action of the previous assembly. They questioned whether this was the intent of the emperor, and on that score they were correct. They affirmed that they could not have two religions side by side in their territories without menace to the public peace, and if their plea was not heard, then 'they must protest and testify publicly before God that they could consent to nothing contrary to his Word.'
Their stand has been variously misinterpreted. In the Protestant camp the emphasis has been all too much on the first word, 'protest', rather than on the second, 'testify'. Above all else, they were confessing their faith... In this protest the Zwinglians and Lutherans were joined." Here I Stand Roland Bainton, pp 317-8 (Lion, 1988)

I labour the matter because modern Protestantism is so far removed from its religious roots as to now be an almost meaningless title. Else why would we have various groups considered to be Protestants who deny some fundamental Protestant and Catholic articles of faith? Why have we now got a professing Christian global mixture of thousands of denominations, some of which have such conflict over what they say the Bible teaches that there can never be any fellowship between them?

Now, if the following definition became the criteria, clarity could come. Protestants should be known for what their forebears in the 1500s did that got them labelled 'Protestants' - they testified publicly before God and society that they could consent to nothing contrary to his Word, the Bible. So important was the Bible to their understanding of the Christian faith that many died dreadful deaths rather than renounce that.

This is no "Standard Definition" of course - not nowadays. But it was the definition in the 1500s when Protestants first emerged as non-Catholic Christians. I'm simply suggesting that if we got back to origins and kept it as simple as that, clarity could come. For a start, Protestants would be recognized as people who attached immense importance to knowing what the Bible teaches, and standing up in public to declare that teaching. All of them. Not just a handful of leaders. That could be revolutionary, don't you think? Of course it would require agreement with such fundamental, ancient statements of belief as the Nicene Creed, which have always been essential to identify Protestants.

You asked for "a Standard Definition". That's my suggestion. None exists as of now. And I don't expect anyone to pay any attention to my suggestion, but there it is, for what it's worth.