The term 'CERTAIN PROTESTANT' can be broken down into two crossword solutions: Lutheran (8 letters) and Unitarian (9 letters). Lutheranism is a branch of Protestant Christianity that was founded by Martin Luther in the 16th century. It is based on the teachings of the Bible and emphasizes the importance of grace and faith. Unitarianism is a liberal religious movement that began in the 18th century and is based on the belief that there is only one God. It is also known for its emphasis on reason and tolerance.