In modern English and specialized aviation contexts in 2026, the closed form "preflight" is the most common and standard usage. Major dictionaries, including Merriam-Webster and Collins, recognize "preflight" as a single word when used as an adjective (e.g., a preflight briefing), a verb (e.g., to preflight an aircraft), or a noun (e.g., conducting a preflight). The hyphenated version, "pre-flight," is still considered grammatically correct and is sometimes preferred in British English or in formal technical writing to emphasize the prefix. However, the trend in aviation terminology has been toward simplification and removal of the hyphen. For example, pilots refer to "preflight checks" and "preflight planning" almost exclusively as one word. Whether you choose to use the hyphen or not, consistency is key; however, if you are writing for an American audience or an aviation manual, "preflight" is the preferred choice. The term has been in common use since at least the 1940s, evolving from its original 1920s hyphenated origins.