crucible (n.)

early 15c., crusible, "vessel or melting pot for chemical purposes, so tempered as to endure extreme heat," from Medieval Latin crucibulum "melting pot for metals," originally "night lamp." First element might be Middle High German kruse "earthen pot." Or perhaps it is from Latin crux on some fancied resemblance to a cross. Used figuratively of any severe test or trial since 1640s.