The athanor's name traces directly to Arabic al-tannur, "the oven," the same word that gives English "tandoor" today, and it entered European alchemical vocabulary through the Latin translations of Arabic scientific and alchemical texts produced from the twelfth century onward, especially the Toledo translation movement. Latin writers gave it a second, more affectionate name, piger Henricus, "Slow Henry," precisely because a well-built athanor, once loaded, would keep a low fire smoldering for a long stretch with little attention, in contrast to a furnace that needed constant stoking.
Because the athanor's whole purpose was sustaining one steady temperature rather than performing any single named operation, it appears throughout medieval and early modern alchemical illustration as the generic furnace standing behind whatever vessel is doing the actual work of the page, the philosophical egg most famously among them. It did not survive into the modern laboratory or industry under its own name or shape; direct-fired, thermostatically controlled ovens and kilns took over the job of holding a long, steady, unattended heat, using electricity or gas rather than banked charcoal, but the underlying need the athanor answered, a heat source that will hold its temperature for hours without a human standing over it, is exactly what a modern kiln controller or oven thermostat is built to do.