Alechemical \al-KEM-ik-uhl\ , adjective;
1. Pertaining to the transformation of something common, usually of little value, into a substance of great worth
2. Relating to a form of chemistry and speculative philosophy practiced in the Middle Ages and the Renaissance concerned principally with discovering methods for transmuting baser metals into gold
The etymology of alchemical obviously derives from the etymology of alchemy, so according to Etymonline.com:
Alchemy dates to the mid-14th century and comes from Old French alkemie which derives from Middle Latin alkimia. The Latin word comes from Arabic al-kimiya which comes from Greek khemeioa. Khemeioa is found in a 4th century text in a Diocletian decree that refers to "the old writings of the Egyptians." It is therefore plausible that the word has roots in Egypt, perhaps from Khemia which is an old name for Egypt that literally means "land of the black earth." Alternatively, it could come from Greek kymatos ("that which is poured out") from khein ("to pour"), which is also related to khymos ("juice, sap"). The most likely situation is that both influences combined to create the word that Latin later adopted. The al- is the Arabic definite article "the."
Most of us know that alchemy was a science that attempted to turn base metals into gold. This is, of course, impossible (at least according to atomic science as we now understand it) and it is not a very good definition of alchemy. In truth, it was a philosophical and spiritual discipline that also involved figuring out how to prepare the "elixir of longevity," and achieving ultimate wisdom. The whole idea of alchemy involved understanding, deconstructing, and reconstructing matter in a way that does not destroy it and therefore gives the alchemist control over that matter and a deep wisdom about it. Alchemy was a forerunner to modern scientific chemistry and gave rise to many substances and processes we still use today (metal working and cosmetics, for example)
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Friday, November 12