An alembic is an alchemical still consisting of two retorts connected by a tube. Technically, the alembic is only the upper part (the capital or still-head), but the word was often used to refer to the entire distillation apparatus.
The word "alembic" has taken on a metaphorical meaning - anything that refines or transmutes, as if by distillation - as in "the alembic of creative thought."
The word, as most alchemical terminology, comes from the Arabic: al-ambiq, "still;" ultimately from the Greek ambix, "cup."
The alembic was developed circa 800 AD by Islamic alchemist Jabir ibn Hayyan.
See also: distilled beverage for history and background.