Will o’ the wisp

Will o’ the wisp is the folkloric name given to the natural phenomenon of marsh gas that sometimes ignites on contact with oxygen. It was known to the Romans as ignis fatuus or false fire. ‘Wisp’ is a word that dates from the 1400s and means a twisted bundle of straw or light twigs that was lit and used as a torch. The medieval legend is that an evil, sinful blacksmith called Will was banned from heaven and condemned to haunt the marshes at night carrying a wisp, hence will o’ the wisp. In other parts of Britain, a similar story grew up about a sinful lad called Jack who was also condemned to the haunt the marshes at night carrying a lantern, hence Jack o’ lantern a synonymous phrase for will o’ the wisp. Will o’ the wisp has been used figuratively since the 19th century to mean a fleeting, shadowy notion or person of little or no substance. See also Jack o’ lantern.