unprecedented

First recorded in 1615–25; un-¹ + precedent + -ed²

The adjective unprecedented is unremarkable in its formation ( un- + precedent + -ed ) and meaning “without precedent, having no precedent; unparalleled.”
What is remarkable about unprecedented is that the two earliest known citations appear with the spelling unpresidented, with an si. The first use of this word appears in a 1641 speech by John Finch, Speaker of the House of Commons (later Lord Keeper of the Great Seal) and a very partisan supporter of King Charles I, and the second recorded use was made by King Charles himself in 1642 in his reply to Parliament. It is not until the following year that we find the first printed instance of this word spelled correctly, with a ce, in a political pamphlet in opposition to Charles I, written by Henry Parker, a strong supporter of the British Parliament.