Secretin
Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.
Ghrelin
Ghrelin was discovered after the ghrelin receptor (called growth hormone secretagogue type 1A receptor or GHS-R) was discovered in 1996 and was reported in 1999. The hormone name is based on its role as a "growth hormone-releasing peptide", with reference to the Proto-Indo-European root "gʰre-", meaning "to grow".