Middle English: the immediate source is unknown, the senses perhaps deriving from different words; probably of Germanic origin and related to flag and flawMiddle English (denoting a wicker hurdle): perhaps of Scandinavian origin and related to Old Norse flaki, fleki 'wicker shield' and Danish flage 'hurdle'late 15th cent. (in the senses 'become languid and (of a garment) fall in folds'): variant of obsolete flack and the verb flag. The current sense dates from the 1940searly 17th cent. (as a noun): of unknown origin; compare with German Flechte in the same sense