A threadlike structure is a thin, elongated strand of material. The term can be used to describe fibers, fibres, and filums, all of which are five-letter words. Fibers are typically composed of natural or synthetic materials, such as cotton, wool, or nylon. Fibres are usually made up of cellulose, which is found in plants. Filum is a Latin word that refers to a single thread or filament. All three terms refer to a thin, threadlike structure.