In 1901, the pharmaceutical company Parke, Davis & Co. (now a subsidiary of Pfizer) registered the trademark Adrenalin to describe a new purified extract from the adrenal glands that was perfected by Japanese chemist Jokichi Takamine. In Europe, people added an e to that, and that's how we got the word adrenaline. Takamine coined the word from Latin ad, meaning "near", renal, meaning "kidneys" and the chemical suffix -ine, because the adrenal glands are located on top of the kidneys. We've seen the prefix ad an inordinate amount of times, and (surprise!) it still comes from a Proto-Indo-European root meaning "to", "near", or "at". Renal, meanwhile, traces to Latin ren, also "kidneys". This has an officially uncertain etymology, but could be from PIE gren, which referred to internal organs in general.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.