1. A peptide hormone, produced by beta cells of the pancreas, and is central to regulating carbohydrate and fat metabolism in the body. (wikipedia.org)
2. A polypeptide hormone secreted by the islets of Langerhans and functioning in the regulation of the metabolism of carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the blood glucose level. (thefreedictionary.com)
3. Any of various pharmaceutical preparations containing this hormone that are derived from the pancreas of certain animals or produced through genetic engineering and are used in the medical treatment and management of diabetes mellitus (type I). (thefreedictionary.com)
4. An animal-derived or synthetic form of this substance used to treat diabetes. (Google Dictionary)
Word origin: Coined in English from Latin insula “island,” so called because the hormone is secreted by the islets of Langerhans in the pancreas.