'alchemistical' originates from the Medieval Latin word 'alchemia', which was derived from the Arabic word 'al-kīmiyā', where 'al-' meant 'the' and 'kīmiyā' meant 'chemistry'.

'alchemia' transformed into the Old French word 'alquemie', and eventually became the modern English word 'alchemy', from which 'alchemistical' is derived.

Initially, it meant 'the art of transmuting metals', but over time it evolved into its current meaning of 'relating to alchemy'.