crucible

A crucible is a melting pot used for extremely hot chemical reactions — the crucible needs to be melt-proof.

Literally, a crucible is a vessel used for very hot processes, like fusing metals. Another meaning of the word is a very significant and difficult trial or test. Scaling Mt. Everest with your legs tied together would be a crucible, as would swimming the English Channel blindfolded. Whether or not to have children is a crucible for many people. The title of Arthur Miller’s play The Crucible is an example of this meaning.

Definitions of crucible
1

n a vessel made of material that does not melt easily; used for high temperature chemical reactions

Synonyms:
melting pot
Type of:
vessel
an object used as a container (especially for liquids)