Nuclear fusion is a process which occurs in. the sun. Hydrogen atoms under a lot of heat and pressure are forced together to make a larger atom of helium
Alchemy is a term used to describe the historical study of elements and matter with the goal of creating an elixir for immortality or trying to change metals into more precious metals.
Alchemy whilst being the study of such wild theories as the transmutation of metals and prolonging of life also had many useful origins of chemistry today from drug design to experimental techniques we still use in the lab today.