There are some words one wonders about. You hear them spoken by others, or read them, but you don't know what they mean, and if you are like me, you are lazy about looking words up. So "crucible" is a word like that for me. I know there is a novel by that name, but I never read it in school or after. But I think maybe I have lived it. Here's what I think it means, then I'm going to google it and tell you what they say it means.
Crucible: First of all I notice right off the bat that the first syllable 'cruc' is the same first syllable as the word 'crucify.' That tells me that I might be on the right track as far as what I think it means. It also shares the same root as the word 'crux' which is the center or heart of the matter. So a crucible would be an experience that penetrates to your core and tests everything that you are made of. It pins you to the cross, but not a wooden cross; rather the cross of you in relation to anything that collides with your deepest truth. A crucible can present a shattering choice, shattering because it means leaving behind things you love, for things you love more.
So here's the definition from Mirriam-Webster:
Full Definition of CRUCIBLE
1: a vessel of a very refractory material (as porcelain) used for melting and calcining a substance that requires a high degree of heat
2: a severe test
3: a place or situation in which concentrated forces interact to cause or influence change or development
Now things are getting very interesting! The word was originally used for a vessel in which substances were melted requiring high heat. Fascinating. Substances are melted, that means we are melted in a crucible. Presumably melted to produce something new. But during the crucible you don't have much of an idea of what that new thing is, but maybe the crucible experience shows you something about why it's needed, the ways you need to grow, who you need to become to be what you truly are.
It's a severe test, as I said. What is tested? One's character is tested: that means a crucible tests who you really are, and what you are made of. It turns you in the direction of your core foundation to see if you are aligned with it. But the responsibility to pass the test is yours and mine, with ample freedom to fail. Which brings us to the third definition. "A crucible is a place or situation in which concentrated forces interact to cause or influence change or development." The forces within a crucible are concentrated. That means the heat's on full blast, melting you, melting you. But you get to decide what the new form will be, and whether it takes on the resemblance of you as the image of God, or instead, as the deepening image of the ego self.