a container of metal or refractory material employed for heating substances to high temperatures.

Metallurgy . a hollow area at the bottom of a furnace in which the metal collects.

a severe, searching test or trial.

a place or situation in which people or ideas are tested severely, often creating sth new or exciting in the process: an alliance forged in the crucible of war

noun

melting pot , cauldron , container , pot , vessel , ordeal , tribulation , visitation , affliction , dish , furnace , test , trial