Indigos are a species of plant with dark blue or purple flowers. Some synonyms for indigos include the terms bluish-purple, deep blue, and violet-blue, all of which describe the same shade of blueish-purple. Other synonyms may refer to the plant itself, including the terms wild indigo, horsefly weed, and border privet. Additionally, the term indigo can also refer to a blue dye that is extracted from the leaves of certain plants. In this context, some synonyms for indigo would include terms like blue dye, indigotin, and natural blue. All of these words describe different aspects of indigos and can be used interchangeably depending on the context in which they are used.