When Middle English speakers borrowed "par aventure" from Anglo-French (in which language it means, literally, "by chance"), it was as an adverb meaning "perhaps" or "possibly." Before long, the word was anglicized to "peradventure," and turned into a noun as well. The adverb is now archaic, though Washington Irving and other writers were still using it in the 19th century ("If peradventure some straggling merchant ... should stop at his door with his cart load of tin ware...." - "A History of New York"). The noun senses we use today tend to show up in the phrase "beyond peradventure" in contexts relating to proving or demonstrating something. The "chance" sense is usually used in the phrase "beyond peradventure of doubt."