It's not a synonym. Unauthorized means not authorized. The works in question contained flawed passages or in other ways were detrimental to the faith. To say they were forbidden just because they were in a common tongue is to do a disservice to the truth.
SD
"William Tyndale was the Captain of the Army of Reformers, and was their spiritual leader. Tyndale holds the distinction of being the first man to ever print the New Testament in the English language. Tyndale was a true scholar and a genius, so fluent in eight languages that it was said one would think any one of them to be his native tongue. He is frequently referred to as the “Architect of the English Language”, (even more so than William Shakespeare) as so many of the phrases Tyndale coined are still in our language today. Tyndale used Erasmus Greek NT to produce the first primary English translation of the New Testament. Forced to flee England, because of the wide-spread rumor that his English New Testament project was underway, causing inquisitors and bounty hunters to be constantly on Tyndale's trail to arrest him and prevent his project. God foiled their plans, and in 1525-1526 the Tyndale New Testament became the first printed edition of the scripture in the English language. Subsequent printings of the Tyndale New Testament in the 1530’s were often elaborately illustrated. Many copies were burned as soon as the Bishop could confiscate them, but many also trickled through to the people and one actually ended up in the bedroom of King Henry VIII. The more the King and Bishop resisted its distribution, the more fascinated the public at large became. The church declared it contained thousands of errors as they torched hundreds of New Testaments confiscated by the clergy, while in fact, they burned them because they could find no errors at all. One risked death by burning if caught in mere possession of Tyndale's forbidden books."