A pot still is a type of still used in distilling spirits such as whisky or brandy. Heat is applied directly to the pot containing the wash (for whisky) or wine (for brandy).
Dioscorides’ ambix (described in his De materia medica) is a helmet-shaped lid for gathering condensed mercury. For Athenaeus (~ 225 C.E.) it is a bottle or flask. For later chemists it denotes various parts of crude distillation devices.