Indigo dye is a popular natural dye that has been used for centuries to color textiles. It is extracted from the leaves of the Indigofera tinctoria plant and has a deep blue hue. The word "indigo" is derived from the Latin word "indicum," which means "from India" since the dye was initially imported from India. There are various synonyms for the word "indigo dye," including woad, pastel, and anil. Woad is a plant that produces blue dye and was widespread in Europe before the importation of indigo. Pastel is a term used to describe a range of pale and muted colors, including indigo. Anil is another term for the indigo plant and its dye.